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Self Assessment Payments on Account: How Do They Work and Who Must Pay Them?

Few things catch new Self Assessment taxpayers off guard quite like their first January bill being far bigger than the tax they actually owed for the year. The culprit is usually payments on account — advance payments toward next year’s tax bill, added on top of what you owe for the year you’re actually filing. It’s not an extra charge or a penalty; it’s simply how HMRC spreads tax payments for people whose income isn’t taxed at source. Understanding how the system works makes it far easier to plan for.

Want help understanding or planning around your payments on account? Book a free 15-minute consultation with Felix Accountants. Book your free call here.

What Are Payments on Account?

Payments on account are advance instalments toward your next tax year’s Self Assessment bill. Rather than waiting until the following January to collect the full amount you’ll owe, HMRC asks most Self Assessment taxpayers to pay roughly half of their expected bill in January and the other half in July, based on the assumption that your income this year will be similar to last year’s.

Who Has to Pay Them?

You’ll generally need to make payments on account if both of the following apply:

  • Your Self Assessment tax bill for the year was more than £1,000
  • Less than 80% of the tax you owed was already collected at source, for example through PAYE

This means most landlords, sole traders and contractors with meaningful untaxed income will fall within the payments on account system, while someone with a small amount of side income taxed mostly through PAYE, or a modest one-off tax bill under £1,000, generally won’t.

How the Two Payments Are Calculated

Each payment on account is equal to 50% of your previous year’s Self Assessment tax bill. So if your tax bill for 2025/26 was £6,000, your payments on account toward 2026/27 would be £3,000 in January 2027 and £3,000 in July 2027 — in addition to any balancing payment due for 2025/26 itself.

A Worked Example

DateWhat’s DueExample Amount
31 JanuaryBalancing payment for the previous tax year + first payment on account for the current year£3,000 (balance) + £3,000 (1st POA) = £6,000
31 JulySecond payment on account for the current year£3,000
Following 31 JanuaryBalancing payment once the actual bill is known + first payment on account for the next yearVaries depending on actual profit

This is why the first year of payments on account often feels disproportionately painful — you’re effectively paying for the previous year and a chunk of the current year at the same time.

What Counts Toward the Payments on Account Calculation

Payments on account are based on your Income Tax and Class 4 National Insurance liability. Capital Gains Tax and student loan repayments are excluded from the payments on account calculation and are instead collected in full as part of your balancing payment. This is a common point of confusion — a large one-off capital gain won’t inflate your payments on account for the following year, but it will need to be paid in full at the balancing payment stage.

Can You Reduce Your Payments on Account?

Yes. If you expect your income for the current year to be lower than the previous year — for example, if a rental property was sold partway through the year, or business income has genuinely dropped — you can apply to reduce your payments on account through your HMRC online account, or by submitting form SA303. This can meaningfully help with cash flow, but it’s worth being careful: if you reduce your payments too far and your actual tax bill turns out higher than the reduced amount, HMRC will charge interest on the shortfall from the original due date, even though you paid the reduced amount on time.

What Happens If You Miss a Payment on Account Deadline?

Interest starts accruing the day after the due date, calculated at the Bank of England base rate plus a fixed percentage. Unlike Self Assessment filing penalties, there’s typically no grace period before interest begins on unpaid tax. If a payment remains outstanding for an extended period, additional late payment penalties can also apply on top of the accruing interest.

How Payments on Account Interact With Making Tax Digital

With Making Tax Digital for Income Tax being introduced from April 2026 for those with qualifying income above £50,000, it’s worth being clear that MTD changes how income and expenses are reported to HMRC — through quarterly digital updates — but it does not change the payments on account system itself. The 31 January and 31 July payment dates remain the same; only the reporting process around them is changing.

Planning Ahead So January Doesn’t Catch You Out

The most effective way to avoid a payments-on-account shock is to set aside a consistent percentage of income throughout the year, rather than treating tax as a single annual event. Many landlords and sole traders find it helpful to transfer roughly a quarter to a third of income into a separate savings account as it’s received, so both the balancing payment and the next payment on account are already covered when the deadlines arrive. Our guide on understanding the UK tax year and key deadlines is a useful companion for mapping out the full annual calendar alongside your payments on account.

How Felix Accountants Can Help

We help landlords and small business owners understand exactly what they’ll owe and when, well before the deadline arrives, and can advise on whether reducing your payments on account makes sense for your circumstances. See our guide on how to file taxes as a landlord for how payments on account fit into the wider Self Assessment picture.

Frequently Asked Questions

Do I have to make payments on account in my first year of trading?

Yes, if your first year’s tax bill is over £1,000 and less than 80% was collected at source, you’ll be required to make payments on account toward the following year, which is why the first January bill can be a shock.

Are payments on account based on my exact current income?

No. They’re based on your previous year’s tax bill, split into two equal instalments, on the assumption your income will be similar. If it isn’t, you can apply to reduce them.

Does Capital Gains Tax affect my payments on account?

No. Capital Gains Tax is excluded from the payments on account calculation and is instead paid in full as part of your balancing payment.

What happens if I reduce my payments on account too much?

If your actual tax bill turns out higher than your reduced payments, HMRC will charge interest on the underpaid amount from the original due date, so reductions should be based on a realistic estimate.

Does Making Tax Digital change when I pay my tax?

No. MTD changes how income and expenses are reported to HMRC through quarterly digital updates, but the 31 January and 31 July payment on account deadlines remain unchanged.

Don’t get caught out by your next Self Assessment bill. Book your free 15-minute consultation with Felix Accountants.


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Let Property Campaign: How Should You Deal With Rental Income From a Property Abroad?

Owning a holiday home in Spain, an apartment in Dubai, or a family property in India can feel entirely separate from your UK tax affairs — especially if local tax has already been paid where the property sits. It’s a common and costly misconception. If you’re UK tax resident, HMRC generally expects you to report your worldwide income, including rent from property overseas, and the Let Property Campaign extends to exactly this situation. Here’s how it works, and what makes overseas disclosures a little different from a straightforward UK-only case.

Not sure how to bring an overseas rental property up to date with HMRC? Book a free 15-minute consultation with Felix Accountants. Book your free call here.

Do You Need to Declare Rent From a Property Abroad?

If you’re resident in the UK for tax purposes — broadly, if you spend more than 183 days a year here, or the UK is your only home — you’re generally taxed on your worldwide income, not just income arising in the UK. This includes rental income from property you own overseas, regardless of whether you’ve already paid local tax on it in the country where the property is located. Many landlords assume that because tax has been paid abroad, or because the income never touches a UK bank account, there’s nothing further to report here. Neither is correct.

Does the Let Property Campaign Cover Overseas Property?

Yes. The Let Property Campaign is open to individual landlords with undeclared residential rental income from property in the UK or abroad. This means a UK resident with an undisclosed overseas rental property is generally eligible to use exactly the same voluntary disclosure route as someone with an undeclared UK buy-to-let, subject to the usual eligibility rules — the campaign is for individuals, not companies or trusts.

Avoiding Double Taxation

A common worry is being taxed twice — once in the country where the property is located, and again in the UK. In practice, the UK has double taxation agreements with most countries, and where tax has genuinely been paid overseas on the same rental income, foreign tax credit relief is generally available to offset that against the UK liability. This doesn’t remove the requirement to report the income in the UK, but it should prevent the same profit being taxed twice in full. Getting this calculation right, particularly where currency conversion and differing tax years are involved, is one of the more technical parts of an overseas disclosure.

Why HMRC’s Reach Now Extends Well Beyond UK Borders

Overseas rental income used to feel harder for HMRC to identify than UK-based lettings. That’s changed substantially. Over 100 countries now participate in the Common Reporting Standard, an international system under which financial institutions automatically share account information across borders. If rent from an overseas property is paid into a foreign bank account, that account’s existence and activity can be reported directly to HMRC’s data-matching systems. Combined with property registry data and international information-sharing agreements, the assumption that an overseas property is effectively invisible to HMRC is now firmly outdated.

Let Property Campaign vs the Worldwide Disclosure Facility

For most individuals with undeclared rental income from a single overseas residential property, the Let Property Campaign remains the appropriate route, and is generally the more specialised and straightforward option. However, HMRC also runs the Worldwide Disclosure Facility, a broader route covering various types of undeclared offshore income and assets beyond just residential letting. Our guide on the common mistakes people make using the Worldwide Disclosure Facility is worth reviewing if your situation extends beyond rental income alone — for example, if it also involves undeclared overseas investment income or foreign bank interest, where the WDF may be the more appropriate channel.

Why Penalties Can Be Higher for Overseas Non-Disclosure

It’s worth being aware that HMRC treats undisclosed offshore income more seriously than equivalent UK-based non-disclosure. Under the “Requirement to Correct” rules, penalties for failing to correct historic offshore tax non-compliance can be significantly higher than standard Let Property Campaign penalties, in some circumstances reaching a much larger proportion of the tax owed. This makes voluntary, proactive disclosure even more valuable for overseas property owners than for UK-only landlords — the gap between coming forward first and being caught later is wider.

How Many Years Do You Need to Go Back?

As with UK property, the look-back period depends on the reason for non-disclosure rather than simply how long the property has been let. Our guide on how many years you need to declare sets out the general framework, and the same principles apply to overseas property, though the practical process of gathering years of foreign records, converted into sterling, often takes longer to prepare than an equivalent UK disclosure.

What You’ll Need to Gather for an Overseas Property Disclosure

  • Rental income received each year, converted to GBP using the correct exchange rate for each period
  • Evidence of any local tax paid on the same rental income, to support a foreign tax credit claim
  • Records of allowable expenses — many of the same categories apply as for UK property, such as agent fees, insurance, and repairs
  • Details of the letting arrangement, including dates and any local property management or agency involved

What About Non-Residents Renting Out UK Property?

The reverse situation also applies. UK residents aren’t the only ones with cross-border obligations — non-residents renting out UK property have their own reporting requirements under the Non-Resident Landlord Scheme, and can also use the Let Property Campaign to correct historic undeclared UK rental income. Our guide on expat tax rules for non-resident landlords covers this side of the picture if it’s more relevant to your situation.

How Felix Accountants Can Help

Overseas disclosures involve extra layers most UK-only cases don’t — currency conversion, foreign tax credits, and sometimes limited or differently formatted local records. We help UK residents bring overseas rental property fully up to date through the Let Property Campaign, calculating what’s genuinely owed after accounting for tax already paid abroad, and managing the disclosure process with HMRC. See our full Let Property Campaign guide for the wider disclosure process this sits within.

Frequently Asked Questions

Do I need to declare rent from an overseas property if I’ve already paid tax on it abroad?

Generally yes, you still need to report it in the UK if you’re UK tax resident, but foreign tax credit relief is usually available so you shouldn’t be taxed twice on the same income.

Can I use the Let Property Campaign for a property outside the UK?

Yes. The campaign covers undeclared residential rental income from property in the UK or abroad, provided you’re an individual landlord rather than a company or trust.

Is it riskier to leave overseas rental income undeclared than UK rental income?

In some respects yes. Penalties for uncorrected offshore non-compliance can be significantly higher than standard UK penalties, and international data-sharing has made overseas income increasingly visible to HMRC.

How does HMRC find out about rental income from a property abroad?

Primarily through the Common Reporting Standard, an international system where financial institutions in over 100 countries automatically share account information, alongside property records and other data-matching sources.

Should I use the Let Property Campaign or the Worldwide Disclosure Facility?

For most cases involving only undeclared rental income from residential property, the Let Property Campaign is usually the appropriate and more specialised route. The Worldwide Disclosure Facility tends to suit broader offshore income or asset disclosures.

Bring your overseas rental property up to date with HMRC. Book your free 15-minute consultation with Felix Accountants.


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Undeclared Rental Income From a Former Home: How Can Landlords Correct Their Tax Position?

It’s one of the most common ways people become landlords without ever really deciding to: you move in with a partner, relocate for work, or upsize to a bigger house, and rather than sell your old property, you rent it out. It feels like a sensible, low-key decision at the time — and often nobody mentions that the rent needs to be declared to HMRC. Years can pass before it becomes clear that this “temporary” arrangement has created a genuine, and growing, tax liability. The good news is that this is a well-recognised situation, and there’s a clear, structured way to correct it.

Rented out your old home without realising you needed to declare it? Book a free 15-minute consultation with Felix Accountants and we’ll help you get back on the right side of HMRC. Find a time here.

Why This Situation Is So Common

Most people who fall into this position never set out to become a landlord. Common scenarios we see regularly include:

  • Moving in with a partner and letting out a previous flat or house rather than selling it
  • Relocating for work and renting the family home while abroad or in another part of the UK
  • Inheriting a property, moving in briefly, and then letting it out once circumstances changed
  • Buying a new main residence and keeping the old one as a rental “for now”

In every one of these cases, the person’s mental model is often “this is still basically my house,” which makes it easy to overlook that HMRC treats rental income exactly the same way regardless of how the letting arrangement came about. Our guide on being an accidental landlord covers this pattern in more depth, including the specific triggers that most often catch people out.

Why the Rent-Only-Covers-the-Mortgage Myth Is So Costly

A particularly common misconception is believing that if the rent received roughly matches the mortgage payment, there’s no taxable profit and therefore nothing to declare. This isn’t correct, for two reasons. First, only the interest element of a mortgage payment is an allowable expense — the capital repayment portion isn’t deductible at all. Second, since 2020, tax relief for mortgage interest on residential lettings held personally has been restricted to a basic-rate tax credit rather than a full deduction against income. This means many landlords who genuinely believed they were breaking even are, in fact, sitting on a taxable rental profit they’ve never reported.

Correcting the Position Through the Let Property Campaign

The Let Property Campaign is HMRC’s dedicated voluntary disclosure route for exactly this situation. It allows individual landlords to come forward, calculate what’s owed across the relevant tax years, and pay it — typically with significantly lower penalties than if HMRC discovers the income independently and opens an enquiry. The process generally involves three stages: notifying HMRC of your intention to disclose, calculating the tax owed for each relevant year (including interest), and submitting a formal disclosure, usually within 90 days of notifying.

Working Out How Many Years to Go Back

The number of years you need to include depends on why the income wasn’t declared, not simply how long you’ve been letting the property. For most people in this situation — where the omission genuinely stemmed from not realising the obligation existed, rather than any attempt to conceal income — the look-back period is typically four to six years. Our detailed guide on how many years you need to declare explains how this is determined and why getting it right matters, since under-disclosing can itself create problems later.

What About the Original Main Residence Relief?

Because the property was once your main home, it’s worth understanding how that history interacts with your tax position going forward, particularly around Capital Gains Tax if you eventually sell. Private Residence Relief can reduce or eliminate Capital Gains Tax for the period the property was genuinely your main residence, plus a final period of ownership, even though it’s since been let out. Our guide on maximising main residence relief explains how this relief interacts with a period of letting, which is a separate but closely related consideration alongside sorting out the undeclared rental income itself.

What If HMRC Has Already Written to You?

If you’ve received a nudge letter from HMRC about rental income, the position changes slightly. A disclosure made after HMRC has already contacted you is classed as “prompted” rather than “unprompted,” which generally attracts a higher penalty percentage than coming forward first. Our comparison of prompted versus unprompted disclosures sets out exactly how the two are treated differently, and it’s still almost always better to respond promptly and constructively than to ignore the letter or delay further.

What You’ll Need to Pull Together

  • The date you moved out and started letting the property
  • Rent received each year, from bank statements or a letting agent’s annual statement
  • Mortgage interest statements for the letting period
  • Records of repairs, insurance, letting agent fees, and any other allowable running costs
  • Details of any period the property was genuinely your main residence, for the Capital Gains Tax position if it’s later sold

If some of this is missing, that’s a common and manageable problem — a reasonable, well-documented estimate is generally acceptable where original records genuinely can’t be recovered.

Why Acting Now Is Better Than Waiting

HMRC’s ability to identify undeclared rental income has grown substantially through data from letting agents, deposit protection schemes, the Land Registry, and information-sharing arrangements with online letting platforms. The longer an undeclared rental arrangement continues, the larger the eventual liability becomes, and the greater the risk that HMRC identifies it independently before you’ve had the chance to disclose voluntarily and secure the lower penalty treatment available for unprompted disclosures.

How Felix Accountants Can Help

We regularly help people in exactly this position — landlords who never intended to be landlords, and who simply want to get their tax affairs straight without unnecessary stress. We’ll help you work out the correct number of years to disclose, calculate what’s owed, and manage the process with HMRC on your behalf through our undisclosed rental income reporting service.

Frequently Asked Questions

Do I need to declare rental income if it just covers my mortgage payment?

Yes. Only the interest portion of a mortgage payment is an allowable cost, and mortgage interest relief for individual landlords is now given as a basic-rate tax credit rather than a full deduction, so many landlords in this position do have a taxable profit even if it doesn’t feel that way.

How many years of rental income will I need to declare for my old home?

This depends on the reason for non-disclosure. Where the omission stemmed from a genuine misunderstanding rather than deliberate concealment, the look-back period is typically four to six years.

Will I lose the tax relief for the years the property was my main home?

No. Private Residence Relief still applies to the period the property was genuinely your main residence, plus a final period of ownership, and this is separate from correcting the undeclared rental income for the letting period.

What if I’ve already had a letter from HMRC about this property?

You can still disclose, but it will generally be treated as a prompted disclosure, which typically carries a higher penalty than an unprompted one. It’s still better to respond and disclose than to ignore the letter.

Is it worth using an accountant for this, or can I do it myself?

You can make a disclosure yourself, but the calculations involving mortgage interest restrictions, allowable expenses and the correct look-back period are easy to get wrong. An accountant experienced with the Let Property Campaign can help ensure the disclosure is accurate and complete the first time.

Ready to put your old home’s rental income right? Book your free 15-minute consultation with Felix Accountants today.


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VAT Flat Rate vs Standard VAT Scheme: Which Could Suit a Small Business?

Once your business is VAT-registered, one of the first practical decisions you’ll face is which VAT scheme to use. The two most common options for small businesses are the standard VAT scheme and the VAT Flat Rate Scheme, and the right choice can genuinely affect both your admin burden and your bottom line. This guide compares how each works, who tends to benefit, and the one rule that catches out a lot of service-based businesses on the Flat Rate Scheme.

Not sure which VAT scheme actually saves you money? Book a free 15-minute consultation with Felix Accountants and we’ll run the numbers for your business. Book your free call here.

How Standard VAT Accounting Works

Under standard VAT accounting, you charge VAT on your sales (output VAT) and reclaim VAT on your business purchases (input VAT). Each quarter, you pay HMRC the difference between the two — output VAT minus input VAT. This means every invoice and receipt genuinely matters, since your VAT bill depends directly on tracking both sides accurately. For businesses with significant purchase costs, such as those buying stock, equipment or materials, this is usually the more financially favourable option, because you’re able to reclaim the VAT you’ve paid out.

How the VAT Flat Rate Scheme Works

The VAT Flat Rate Scheme (FRS) simplifies the calculation considerably. You still charge customers VAT at the standard rate — usually 20% — but instead of separately tracking input VAT on purchases, you pay HMRC a single fixed percentage of your VAT-inclusive turnover. The percentage is set by HMRC according to your business sector and is always below 20%, so the gap between what you charge and what you hand over effectively stays in the business.

For example, if your sector’s flat rate is 12% and you invoice a client £10,000 plus £2,000 VAT (a total of £12,000), you’d pay HMRC 12% of £12,000, which is £1,440, keeping the remaining £560 rather than reclaiming input VAT separately.

To join the scheme, your VAT-taxable turnover generally needs to be £150,000 or less (excluding VAT) in the next 12 months, and you must leave once your total VAT-inclusive turnover exceeds £230,000 on the anniversary of joining, or if you expect it to exceed that figure within the next 12 months.

The First-Year Discount

If you’re in your first year of VAT registration, HMRC applies a 1% discount to your flat rate percentage. So a business with a standard sector rate of 12% would pay just 11% during that first year, from the date of VAT registration until the first anniversary of joining the scheme.

The Limited Cost Trader Rule: Why the Flat Rate Scheme Can Backfire

This is the single most important rule to understand before choosing the Flat Rate Scheme. If your business spends very little on goods — broadly, less than 2% of your VAT-inclusive turnover, or under £250 per quarter — you’re classed as a “limited cost trader” and must apply a flat rate of 16.5%, regardless of your actual sector. Because 16.5% of VAT-inclusive turnover is very close to the full 20% VAT you’re charging, the scheme can end up leaving you with barely any benefit, or in some cases costing more than standard VAT accounting would have.

This catches out a lot of consultants, contractors, agencies and other service businesses with genuinely low goods spend — think office supplies and a laptop, rather than stock or materials. If that describes your business, it’s worth running the comparison carefully before committing to the Flat Rate Scheme.

What You Can Still Reclaim Under the Flat Rate Scheme

There’s one notable exception to the “no input VAT reclaim” rule on the Flat Rate Scheme: capital assets costing £2,000 or more (including VAT) can still have their input VAT reclaimed separately, even while you’re on the scheme. This matters if you’re planning a larger one-off purchase, such as equipment or machinery, as it can meaningfully change the maths.

Comparing the Two: A Practical Framework

FactorStandard VAT SchemeVAT Flat Rate Scheme
Admin burdenHigher — every purchase and sale trackedLower — one percentage applied to turnover
Reclaiming VAT on purchasesYes, in full (subject to normal rules)No, except capital assets over £2,000
Best suited toBusinesses with significant purchase/stock costsLow-cost service businesses not caught by the 16.5% rule
Risk factorMore record-keeping errors possibleLimited cost trader rule can erode the benefit

Which Businesses Tend to Benefit From the Flat Rate Scheme?

  • Service businesses with a sector flat rate meaningfully below 20% that aren’t caught by the limited cost trader rule
  • Businesses that want simpler quarterly VAT returns and are willing to accept a slightly less precise calculation in exchange for reduced admin
  • New businesses in their first year of VAT registration benefiting from the 1% discount

Which Businesses Tend to Benefit From Standard VAT Accounting?

  • Businesses with regular, significant purchases where reclaiming input VAT makes a real financial difference
  • Businesses whose main activity would place them in, or close to, the 16.5% limited cost trader category under the Flat Rate Scheme
  • Businesses that want the VAT return to reflect the actual, precise VAT position rather than a fixed-percentage approximation

Don’t Forget Making Tax Digital

Regardless of which VAT scheme you choose, VAT-registered businesses are required to keep digital records and file VAT returns through Making Tax Digital-compatible software. This has applied to all VAT-registered businesses for some time now, so the choice between schemes doesn’t affect whether MTD applies — only how the underlying VAT calculation is worked out.

How This Applies to Property and Landlord Businesses

Most residential letting income is exempt from VAT, so many individual landlords never need to register at all. However, property developers, those providing furnished holiday lettings on a commercial scale, or businesses with a mix of taxable and exempt property income can face more complex VAT decisions. Our guide on VAT and property in the UK and our article on VAT implications for property developers and investors cover this in more detail if your situation involves property alongside a wider small business.

How Felix Accountants Can Help

Choosing between the Flat Rate Scheme and standard VAT accounting isn’t a one-size-fits-all decision — it depends on your actual sector rate, your typical spending on goods, and your growth plans. We run the comparison for clients using real business figures rather than rules of thumb, and handle the registration, scheme selection and ongoing VAT return filing. See our wider taxation services for how we support small businesses beyond VAT.

Frequently Asked Questions

Can I switch between the Flat Rate Scheme and standard VAT accounting?

Yes, you can leave the Flat Rate Scheme at any time, though once you leave you generally can’t rejoin for at least 12 months. Moving to the Flat Rate Scheme from standard VAT is also possible if you meet the eligibility criteria.

What is a limited cost trader?

A limited cost trader is a business that spends less than 2% of its VAT-inclusive turnover on goods (not services) in a VAT period, or less than £250 per quarter. Limited cost traders must apply a 16.5% flat rate, regardless of their actual business sector.

Do I still charge customers 20% VAT on the Flat Rate Scheme?

Yes. The flat rate percentage only affects how much VAT you hand over to HMRC, not the rate you charge customers, which remains the normal rate applicable to your goods or services.

Is the Flat Rate Scheme always simpler, even if it isn’t cheaper?

Generally yes, since you don’t need to analyse every purchase invoice for VAT. However, “simpler” doesn’t always mean “cheaper,” so it’s worth weighing the admin saving against the potential extra VAT cost, particularly under the 16.5% limited cost trader rate.

Does my VAT scheme choice affect Making Tax Digital requirements?

No. Making Tax Digital applies to all VAT-registered businesses regardless of which VAT scheme they use — it governs how records are kept and returns are filed, not which scheme calculates the VAT owed.

Let’s work out which VAT scheme actually suits your business. Book your free 15-minute consultation with Felix Accountants today.


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Corporation Tax Accounting Periods Explained for UK Companies

Every UK limited company has a Corporation Tax accounting period, and understanding exactly what it is — and how it differs from your company’s financial year — is essential to avoiding late filing penalties and interest charges. It’s a surprisingly common source of confusion, particularly for new directors, because the accounting period isn’t always the same length as the company’s financial year shown at Companies House. This guide sets out clearly what a Corporation Tax accounting period is, how it’s set, and what deadlines follow from it.

Not sure when your Corporation Tax is actually due? Book a free 15-minute consultation with Felix Accountants and we’ll confirm your exact deadlines. Book your free call here.

What Is a Corporation Tax Accounting Period?

A Corporation Tax accounting period is the period HMRC uses to calculate how much Corporation Tax your company owes. It’s usually 12 months long and generally matches your company’s financial year, which runs to your accounting reference date set at Companies House. However, the two aren’t automatically identical — HMRC’s rules cap a single Corporation Tax accounting period at 12 months, so if your company’s financial year is longer than 12 months (which can happen in a company’s first year of trading), HMRC splits it into two separate accounting periods for tax purposes.

Financial Year vs Accounting Period: What’s the Difference?

These two terms are often used interchangeably, but they serve different purposes:

  • Financial year (accounting reference period): the period covered by your statutory accounts, filed at Companies House. This can be up to 18 months for a company’s first set of accounts.
  • Corporation Tax accounting period: the period HMRC uses to assess Corporation Tax. This is capped at 12 months, so a longer financial year is split accordingly.

For example, a company incorporated on 1 July 2025 with an accounting reference date of 31 March 2026 would have a first financial year of nine months (1 July 2025 to 31 March 2026), which in this case fits within the 12-month cap, so financial year and accounting period would match. But a company with a longer first period — say, 15 months from incorporation to its first accounting reference date — would need to split that into a 12-month Corporation Tax accounting period followed by a shorter second period covering the remaining months, each requiring its own calculation and, where applicable, its own CT600 return.

How Your First Accounting Period Is Set

Your first Corporation Tax accounting period begins on the date your company starts trading, not necessarily the date it was incorporated. Many companies are incorporated some time before they actually begin trading — for example, a property investment company might be set up months before it acquires its first property. Corporation Tax obligations, including the requirement to register with HMRC, generally begin once trading activity actually starts, so it’s important to notify HMRC within three months of trading commencing.

If you’re setting up a company to hold or invest in property, our guide on property investment through a limited company covers some of the wider considerations around structuring, alongside the accounting period rules covered here.

The Three Key Deadlines That Follow From Your Accounting Period

Once your accounting period is established, three separate deadlines follow from its end date:

  • Corporation Tax payment: due 9 months and 1 day after the end of the accounting period
  • Company Tax Return (CT600): due 12 months after the end of the accounting period
  • Companies House annual accounts: due 9 months after the end of the financial year for most private companies (21 months from incorporation for a first set of accounts)

Note that the tax payment deadline actually falls before the CT600 filing deadline — a common point of confusion. For example, for an accounting period ending 31 March 2026, Corporation Tax would be due by 1 January 2027, while the CT600 return wouldn’t be due until 31 March 2027. Directors sometimes assume that because the return isn’t due yet, the payment isn’t either, which can lead to interest charges on genuinely late tax.

Why Splitting an Accounting Period Matters in Practice

When a financial year longer than 12 months is split into two Corporation Tax accounting periods, each period requires its own profit calculation, its own set of allowances and reliefs applied proportionately, and potentially its own CT600 submission. This most commonly affects newly incorporated companies with an unusually long first trading period, and it’s an area where getting the split wrong can lead to an incorrect tax calculation or a missed filing obligation for the second, shorter period. This is particularly relevant for companies formed to hold buy-to-let or investment property, where the gap between incorporation and the first accounting reference date can sometimes exceed 12 months.

Can You Change Your Accounting Period?

Yes, a company can shorten or extend its accounting reference date at Companies House, which in turn affects the Corporation Tax accounting periods that follow. This might be done to align the company’s year-end with a parent company, a calendar year, or simply for administrative convenience. Any change should be considered carefully, since it can affect both the Companies House filing deadline and how HMRC treats the corresponding tax periods, and once shortened, some restrictions apply to changing it again too frequently.

What Happens if You Miss an Accounting Period Deadline?

Missing the Companies House accounts deadline triggers an automatic penalty, starting from £150 for filings up to one month late and rising with the length of the delay, doubling if you were also late the previous year. Separately, missing the CT600 filing deadline triggers its own fixed penalties from HMRC, and missing the tax payment deadline results in daily interest accruing on the outstanding amount. Because these are three distinct obligations with three distinct deadlines, it’s entirely possible to file your accounts on time but still incur penalties for a late Corporation Tax payment, or vice versa.

Dormant Companies Aren’t Exempt

Even if your company hasn’t started trading, it still has an accounting reference period for Companies House purposes and must file dormant accounts on the same schedule as a trading company. Once trading does begin, the Corporation Tax accounting period clock starts, and HMRC registration becomes necessary within three months.

How Felix Accountants Can Help

We help directors of trading companies and property investment companies alike get their accounting periods, deadlines and filings right from day one, whether that’s registering a newly trading company with HMRC, managing a split accounting period in year one, or simply confirming when your next Corporation Tax payment is actually due. See our wider business tax services for how we support companies through the full filing cycle.

Frequently Asked Questions

Is my Corporation Tax accounting period the same as my financial year?

Usually, yes, but not always. A Corporation Tax accounting period can never exceed 12 months, so if your company’s financial year is longer than 12 months, it will be split into two separate accounting periods for Corporation Tax purposes.

When does my first accounting period start?

Your first Corporation Tax accounting period begins when your company starts trading, which is not necessarily the same as its incorporation date.

What’s the deadline to pay Corporation Tax?

Corporation Tax is generally due 9 months and 1 day after the end of your accounting period, which is earlier than the deadline to file your CT600 return.

Do I need to file a CT600 if my company hasn’t traded yet?

If your company is genuinely dormant, you’ll still need to file dormant accounts at Companies House, but a CT600 is only required once the company has started trading and been registered with HMRC for Corporation Tax.

Can I change my company’s accounting reference date?

Yes, you can shorten or extend your accounting reference date via Companies House, though this affects your future Corporation Tax accounting periods and filing deadlines, so it’s worth getting advice before making the change.

Get clarity on your company’s exact filing deadlines. Book your free 15-minute consultation with Felix Accountants.


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Articles Articles Blogs Let Property Campaign

Bookkeeping for Landlords: How to Organize Rental Income and Property Records

Good bookkeeping is the difference between a stress-free Self Assessment season and a scramble every January to remember which repair bill belonged to which property. For UK landlords, keeping rental income and expenses organised throughout the year isn’t just good practice — with Making Tax Digital for Income Tax rolling out from April 2026, it’s becoming a legal requirement for many. This guide sets out a practical, low-effort system for organising your rental records properly, whether you own one buy-to-let or a small portfolio.

Want help setting up a bookkeeping system that actually works for your properties? Book a free 15-minute consultation with Felix Accountants. Find a time here.

Why Bookkeeping Matters More Than Ever for Landlords

Historically, many landlords managed with a shoe-box of receipts and an annual spreadsheet pulled together just before the Self Assessment deadline. That approach is becoming increasingly risky, and not just because it’s stressful. Making Tax Digital for Income Tax Self Assessment is being introduced from 6 April 2026 for landlords and sole traders with qualifying income over £50,000, dropping to £30,000 from April 2027, and further down again in later years. Under STD, you’ll need to keep digital records of rental income and expenses and submit quarterly updates to HMRC, rather than a single annual return. Our guide on the top five things landlords need to know about STD covers the roll out in more detail.

Separate Your Property Finances From Personal Finances

The single most effective bookkeeping habit is running rental income and expenses through a dedicated bank account, separate from your personal spending. This doesn’t need to be a business account if you’re a sole individual landlord — a simple second personal current account is enough for most people with one or two properties. The benefit is immediate clarity: every transaction in that account relates to the property, so you’re not trying to remember months later whether a payment was rent, a personal transfer, or something else entirely.

What Records You Actually Need to Keep

At a minimum, landlords should retain records covering:

  • Rental income: the date, amount, and source of every rent payment received
  • Mortgage interest: statements showing the interest element of mortgage payments, which is treated differently from the capital repayment for tax purposes
  • Repairs and maintenance: invoices and receipts, kept separate from any capital improvement costs
  • Letting agent fees and management costs
  • Insurance: landlord and buildings insurance premiums
  • Ground rent and service charges, where applicable to leasehold properties
  • Utility bills, where paid by the landlord rather than the tenant
  • Travel costs genuinely incurred managing or maintaining the property

Our detailed guide to allowable expenses for property investors breaks down what can and can’t be claimed against rental income, and our broader guide to landlord accounting covers how these figures ultimately feed into your tax return.

Choose a System That Matches Your Portfolio Size

Bookkeeping doesn’t need to be complicated to be effective. A sensible approach scales with how many properties you manage:

  • One property, straightforward finances: a well-structured spreadsheet with a tab per property, updated monthly, may be sufficient — provided it captures every transaction with a date, amount, category and property reference.
  • Multiple properties or growing complexity: dedicated landlord bookkeeping software (many of which are STD-compatible) makes it far easier to track income and expenses per property, generate reports, and export figures at year end.
  • Portfolio landlords or those approaching the STD threshold: cloud accounting software linked directly to your bank account removes most manual data entry and creates the kind of transaction-level digital trail STD requires.

Whichever system you choose, the golden rule is consistency: recording transactions weekly or monthly, rather than trying to reconstruct a year’s worth of activity in one sitting.

Getting Ready for Making Tax Digital

If your combined property and self-employment income is likely to exceed £50,000, you’ll need STD-compatible software from April 2026 to keep digital records and submit quarterly updates, followed by a Final Declaration each year. Our April 2026 STD deadline guide explains the practical steps to prepare. Even if you’re currently below the threshold, it’s worth adopting STD-style habits now, since the qualifying income threshold is set to fall to £30,000 from April 2027 and is expected to reduce further in subsequent years, gradually bringing more landlords into scope.

Common Bookkeeping Mistakes Landlords Make

  • Mixing personal and rental transactions in the same bank account
  • Confusing capital improvements (which aren’t deductible against rental income in the same way as repairs) with genuine repair and maintenance costs
  • Losing receipts for cash payments to tradespeople
  • Failing to record the mortgage interest figure separately, which matters given the restricted way interest relief is now given to individual landlords
  • Waiting until January to reconcile a full year of transactions in one go

Our article on the top five bookkeeping mistakes to avoid covers several of these in more depth, alongside practical fixes.

A Simple Monthly Routine That Works

Rather than an elaborate system, most landlords do well with a short monthly routine:

  1. Log into your dedicated property bank account and record any new rent received
  2. Enter any expenses paid that month, categorising each one (repairs, insurance, agent fees, etc.)
  3. Photograph or scan paper receipts and store them digitally, linked to the relevant transaction
  4. Note any capital works separately from routine repairs
  5. Once a quarter, review the running totals against your budget or previous year, to catch anything unusual early

Twenty minutes a month is almost always less painful — and far more accurate — than several hours of reconstruction under deadline pressure.

How Felix Accountants Can Help

We help landlords set up bookkeeping systems that fit their portfolio, whether that’s a simple spreadsheet template or full cloud accounting software integration ahead of Making Tax Digital. We also review historic records to make sure nothing has been missed, and prepare Self Assessment returns based on properly organised figures rather than last-minute estimates. See our guide on how to file taxes as a landlord for how good bookkeeping feeds directly into a smoother tax return.

Frequently Asked Questions

Do I need a separate bank account for my rental property?

It isn’t a legal requirement for individual landlords, but it’s strongly recommended. A dedicated account makes it far easier to track income and expenses accurately and separates rental activity from personal spending.

How long should I keep landlord bookkeeping records?

HMRC generally requires records to be kept for at least five years after the 31 January submission deadline for the relevant tax year, so records should typically be retained for around six years in total.

Do I need accounting software as a landlord, or is a spreadsheet enough?

A well-maintained spreadsheet can be sufficient for a single property, but landlords approaching the Making Tax Digital threshold will need STD-compatible software to keep digital records and submit quarterly updates.

What’s the difference between a repair and a capital improvement for bookkeeping purposes?

A repair restores something to its original condition (such as fixing a broken boiler) and is generally deductible against rental income. A capital improvement enhances the property beyond its original state (such as adding an extension) and is treated differently for tax purposes.

When does Making Tax Digital start affecting landlords?

STD for Income Tax Self Assessment begins on 6 April 2026 for landlords and sole traders with qualifying income above £50,000, with the threshold reducing in later years to bring more landlords into scope.

Get your rental bookkeeping under control before the next deadline. Book your free 15-minute consultation with Felix Accountants today.


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Articles Blogs Let Property Campaign News

Let Property Campaign Disclosure: How Should Landlords Deal With Missing Rental Records?

One of the most common reasons landlords put off making a Let Property Campaign disclosure isn’t reluctance — it’s fear that they simply don’t have the paperwork to back it up. Old tenancy agreements have been lost, bank accounts have been closed, and receipts for repairs from six years ago were never kept. The reassuring truth is that missing records don’t stop you from making a valid disclosure; HMRC expects landlords in this position and accepts carefully reasoned estimates, provided they’re built on a sensible method rather than guesswork.

Missing paperwork doesn’t have to hold up your disclosure. Book a free 15-minute consultation with Felix Accountants and we’ll help you map out exactly what you can reconstruct. Grab a free slot here.

Why Missing Records Are So Common Among Landlords Disclosing Under the LPC

Most landlords who end up using the Let Property Campaign weren’t running a professional letting business from day one. Many became landlords by accident — inheriting a property, relocating for work, or renting out a former family home — and never set up formal bookkeeping. Years later, when it’s time to disclose, bank statements have often been archived beyond easy online access, letting agents have changed hands, and receipts were simply thrown away. This is normal, and it’s exactly the scenario HMRC’s disclosure process is built to accommodate.

Start With What You Can Actually Access

Before assuming records are gone for good, it’s worth checking a few sources that are often more complete than landlords expect:

  • Online banking archives: most UK banks retain digital statements for 6–7 years and can often provide older statements on request, sometimes for a small fee
  • Letting agent portals or year-end statements: agents typically issue annual income summaries, which are far easier to request than reconstructing every transaction
  • Mortgage statements: useful for establishing the interest paid, which is a major allowable cost
  • Insurance renewal documents: confirm landlord insurance costs and the dates the property was actually let
  • Land Registry and conveyancing paperwork: confirms purchase date, sale date (if applicable), and ownership history

Our guide to record keeping sets out the categories of documents HMRC typically expects landlords to retain, and is a useful checklist even when working backwards from an incomplete starting point.

When Records Genuinely Don’t Exist: Building a Reasonable Estimate

Where source documents can’t be recovered, HMRC allows landlords to use reasonable estimates, as long as the method is transparent and defensible. A sound approach usually involves:

  • Establishing the letting period from tenancy start/end dates, Land Registry records, or correspondence with a former letting agent
  • Using average local market rents for a comparable property over the relevant years as a cross-check against any partial records you do have
  • Applying a consistent, conservative approach to expenses — only claiming costs you can reasonably evidence or that are typical and proportionate for the property type
  • Documenting the assumptions behind every estimate in writing, so the methodology can be explained if HMRC asks questions later

This is where working with an accountant experienced in Let Property Campaign disclosures makes a real difference. We’ve supported landlords who arrived with almost nothing beyond a mortgage statement and a rough idea of when tenants moved in, and helped them build a disclosure that HMRC accepted without further challenge.

Missing Records Don’t Change Your Look-Back Period

It’s worth being clear that having incomplete records doesn’t reduce how many years you need to disclose. The look-back period is determined by the reason the income wasn’t declared — careless error, failure to take reasonable care, or deliberate non-disclosure — not by how much paperwork survives. Our article on how many years you need to declare explains this in more detail, and it’s a good starting point before you begin reconstructing figures, so you know exactly which tax years to focus on.

The 90-Day Window and Why Preparation Matters

Once you notify HMRC of your intention to disclose under the Let Property Campaign, you generally have 90 days to submit the full disclosure and calculate what’s owed. Trying to reconstruct several years of missing records within that window, under time pressure, is far harder than starting the reconstruction work before you notify HMRC. Our 90-day deadline prep guide walks through how to use that period efficiently if you’ve already notified, but the ideal approach is to begin gathering what you can before you formally start the clock.

What Counts as a Reasonable Excuse — and What Doesn’t

Missing records themselves aren’t usually accepted as a reason not to disclose at all, but the circumstances behind why records went missing can matter for how HMRC views your overall behaviour. Genuinely losing paperwork in a house move, a bereavement, or simply never having set up formal bookkeeping as an accidental landlord is treated very differently from deliberately destroying evidence. Being upfront about why records are incomplete, rather than presenting rough figures as if they were exact, tends to support a smoother disclosure.

Common Mistakes to Avoid When Records Are Incomplete

  • Rounding figures without any supporting logic, rather than using a documented estimation method
  • Ignoring years where you’re unsure of the exact rent, hoping HMRC won’t notice — this significantly increases risk if discovered later
  • Claiming expenses you can’t reasonably evidence or that seem disproportionate to the size of the letting
  • Waiting indefinitely to “find better records” instead of starting the disclosure with a reasonable, well-documented estimate

See our broader guide on the top bookkeeping mistakes landlords make for related pitfalls worth avoiding going forward.

How Felix Accountants Helps When Your Records Are Incomplete

We regularly work with landlords who come to us with partial, patchy, or almost non-existent records for the years in question. Our process involves piecing together what’s available, applying recognised estimation techniques where genuine gaps exist, and preparing a disclosure that stands up to scrutiny. You can read more in our LPC disclosure guide or get in touch directly to talk through your specific situation.

Frequently Asked Questions

Can I make a Let Property Campaign disclosure without any bank statements?

Yes, in principle. If bank statements aren’t available, other evidence such as letting agent statements, tenancy agreements, or a reasonable, documented estimate based on comparable market rents can be used instead.

Will HMRC reject my disclosure if some figures are estimates?

Not usually, provided the estimates are reasonable, consistently applied, and clearly explained as estimates rather than presented as exact figures without qualification.

Should I wait until I’ve found all my missing records before notifying HMRC?

Generally no. It’s better to begin the record-reconstruction process first, then notify HMRC once you have a workable picture, since the 90-day disclosure window starts as soon as you notify.

Does having incomplete records mean I’ll face higher penalties?

Not on its own. Penalties are primarily driven by whether the disclosure is prompted or unprompted and the underlying behaviour (careless versus deliberate), not simply by the state of your paperwork.

Can an accountant help reconstruct years of missing rental records?

Yes, this is one of the most valuable parts of working with an experienced property accountant during a Let Property Campaign disclosure, as we can apply consistent, defensible methods across multiple tax years.

Don’t let missing paperwork stop you from disclosing. Book your free 15-minute consultation with Felix Accountants and we’ll help you build a disclosure that works with what you actually have.


 

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Articles Articles Corporation Tax

Accounting Profit vs Taxable Profit: Corporation Tax Explained

If you’ve ever looked at your company’s profit and loss account and then been surprised by the Corporation Tax bill that follows, you’re not alone. The profit in your accounts and the profit HMRC actually taxes are rarely the same figure, and understanding why is one of the most useful things a director can learn about how Corporation Tax actually works.

Want a second opinion on your Corporation Tax computation before you file? Book a free 15-minute consultation with Felix Accountants and we’ll take a look.

What Is Accounting Profit?

Accounting profit is the figure shown in your statutory accounts, prepared under standard accounting frameworks such as FRS 102 or FRS 105. It reflects your income less all costs recognised during the accounting period, including things like depreciation, which spreads the cost of an asset over its useful life for accounting purposes.

What Is Taxable Profit?

Taxable profit — more precisely, “taxable total profits” for Corporation Tax purposes — starts with your accounting profit and adjusts it according to tax law. Some costs that are perfectly valid in your accounts simply aren’t deductible for tax, and some tax reliefs don’t appear in your accounts at all. The result, after these adjustments, is the figure your Corporation Tax is actually calculated on.

Why Depreciation Gets Added Back

Depreciation is an accounting estimate of how an asset loses value over time, and estimates aren’t something tax law is willing to rely on directly. Instead, depreciation is added back in full in the tax computation, and capital allowances — a set of HMRC-defined rates and allowances — are used instead to give tax relief on qualifying capital expenditure. The Annual Investment Allowance, for example, currently allows many businesses to deduct the full cost of qualifying plant and machinery in the year of purchase, up to a set limit, with writing down allowances covering amounts above that.

Common Disallowable Expenses

Beyond depreciation, several other costs that appear in your accounts must be added back because they aren’t allowable for Corporation Tax:

  • Client entertainment costs
  • Fines and penalties, including parking tickets and HMRC penalties
  • Costs that don’t meet the “wholly and exclusively” test for business purposes
  • Certain provisions that haven’t yet crystallised into an actual liability

For a fuller list of what is and isn’t deductible for a limited company, see our guide to allowable limited company expenses.

A Worked Example

ItemAmount
Profit per accounts£60,000
Add back: depreciation+£8,000
Add back: client entertaining+£1,200
Less: capital allowances-£6,500
Taxable total profits£62,700

Notice that the taxable figure here is higher than the accounting profit, even though the company hasn’t earned any additional cash — it’s purely the effect of the add-backs and reliefs working differently in the two calculations. In other cases, generous capital allowances can push taxable profit below accounting profit instead.

Why This Distinction Matters for Directors

Understanding the gap between accounting and taxable profit matters for more than just curiosity. It affects how much cash you should be setting aside for your Corporation Tax bill, and it’s also a completely separate question from how much profit is legally available to pay out as dividends, which is governed by company law and your accounting profit and reserves, not your tax computation. Paying dividends from profits that don’t actually exist can result in an illegal dividend — our guide on illegal dividends explains this risk in more detail.

Common Misunderstandings

  • Assuming your Corporation Tax bill should match a simple percentage of your accounting profit
  • Forgetting that capital expenditure isn’t deducted as it’s spent, but relieved through capital allowances instead
  • Treating distributable reserves and taxable profit as the same thing when deciding on dividends
  • Missing available reliefs, such as R&D relief, because they don’t automatically appear in the accounting figures

How Felix Accountants Can Help

We prepare Corporation Tax computations that correctly reconcile your accounting profit to your taxable profit, make sure you’re claiming every allowance and relief you’re entitled to, and help you plan cash flow around your actual tax liability rather than guesswork.

Frequently Asked Questions

Why is my Corporation Tax bill higher than expected based on my accounts?

This usually happens because disallowable expenses, like depreciation or client entertaining, have been added back in the tax computation, increasing your taxable profit above your accounting profit.

Do capital allowances always reduce my tax bill more than depreciation would?

Not necessarily in every year, but capital allowances are the only mechanism HMRC recognises for tax relief on capital expenditure, so understanding and claiming them correctly is essential regardless of how they compare to your accounting depreciation charge in any given year.

Can I pay dividends based on my accounting profit even if my taxable profit is lower?

Dividends must be paid from distributable reserves under company law, which relate to your accounting position, not your taxable profit figure. The two calculations serve different purposes and shouldn’t be confused when deciding what can legally be paid out.

Does every company need a formal tax computation separate from its accounts?

Yes. Even small companies need to prepare a Corporation Tax computation that adjusts accounting profit for tax purposes as part of the CT600 filing process, regardless of how straightforward the underlying accounts are.

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Articles Articles Blogs Self Assessment Taxation Services

What Happens If You Discover an Error in a Previous UK Tax Return?

Spotting a mistake on a tax return you’ve already submitted is more common than you might think — a missed expense, an omitted source of income, or a figure that simply doesn’t add up. The important thing is what you do next, because HMRC treats a self-corrected error very differently from one it uncovers itself.

Not sure whether you’re still within the amendment window, or how to approach HMRC about an older error? Book a free 15-minute consultation with Felix Accountants and we’ll help you work out the best next step.

Step One: Work Out Which Deadline Applies

How you correct the error depends on how long ago you filed the return in question.

Within 12 Months of the Filing Deadline

If you’re within 12 months of the normal Self Assessment filing deadline for that return, you can simply amend it yourself. For an online return, log back into your HMRC account, update the relevant figures, and resubmit — the system recalculates your bill automatically, showing whether you owe more or are due a refund. For example, a 2024/25 return filed by the 31 January 2026 deadline can generally be amended up to 31 January 2027.

More Than 12 Months After the Deadline

Once the 12-month window has closed, you can no longer amend the return online. Instead, you’ll need to write to HMRC explaining the correction, or make a formal overpayment relief claim if the error means you paid too much tax. Overpayment relief claims can generally be made up to four years after the end of the tax year the return relates to.

What to Include in a Written Correction or Overpayment Relief Claim

  • The tax year the correction relates to
  • A clear explanation of what was wrong and why
  • The amount you believe was overpaid or underpaid
  • Supporting evidence (invoices, statements, calculations)
  • A signed declaration confirming the details are correct and complete to the best of your knowledge

If the Error Means You Owe More Tax

If correcting the mistake increases your tax bill, it’s best to notify HMRC and pay the difference as soon as you’re aware of it. Interest accrues from the original due date, and coming forward yourself, before HMRC identifies the discrepancy independently, generally puts you in a much stronger position on penalties than waiting to be caught out. This is the same underlying principle behind voluntary disclosure routes like the Let Property Campaign for landlords with undeclared rental income specifically.

If the Error Means You Overpaid

If you’re due a refund, amending within the 12-month window is the most straightforward route — HMRC recalculates your position and processes the repayment. Outside that window, an overpayment relief claim achieves the same result but requires a more formal written submission with supporting evidence.

Genuine Mistakes vs Careless or Deliberate Errors

HMRC distinguishes between an honest, reasonable mistake and one caused by carelessness or deliberate action, and this distinction affects whether a penalty applies at all. If you took reasonable care and made a genuine error in good faith, you’re unlikely to face a penalty for correcting it — HMRC generally responds far more favourably to taxpayers who put things right themselves. If the error was significant, spanned several years, or involved undeclared income you knew about, professional advice is worth getting before you approach HMRC, since the correct classification affects both the penalty and how many years need correcting.

What If HMRC Corrects the Error First?

HMRC can amend a return itself within nine months of the date you filed it, typically to correct obvious errors, and will notify you of any change. If HMRC identifies a more significant discrepancy through a compliance check, the process moves from a simple correction into a formal enquiry, and the potential penalties for the same underlying mistake are usually higher than if you’d corrected it proactively.

A Practical Example

Suppose you filed your 2023/24 return in January 2025 and later realise, in mid-2026, that you forgot to include some rental income. Since more than 12 months have passed since the 31 January 2025 deadline, you can’t amend the return online — you’d need to write to HMRC, or, if the omission relates to rental income specifically, consider whether the Let Property Campaign disclosure process is the more appropriate route, since it’s specifically designed for this kind of correction.

How Felix Accountants Can Help

Whether you’re inside the 12-month amendment window or need to make a formal overpayment relief claim or voluntary disclosure, we’ll help you work out the right process, prepare accurate figures, and manage the correspondence with HMRC on your behalf.

Frequently Asked Questions

How long do I have to amend a Self Assessment tax return?

You generally have 12 months from the normal filing deadline for that tax year. For example, a return with a 31 January 2027 deadline can usually be amended up to 31 January 2028.

What is overpayment relief?

Overpayment relief is a formal claim you can make to recover tax you’ve overpaid, once the standard 12-month amendment window has passed. It must generally be made within four years of the end of the relevant tax year and requires a written submission with supporting evidence.

Will I be penalised for correcting my own mistake?

If the error was a genuine mistake made despite taking reasonable care, a penalty is unlikely. Penalties are more commonly applied where HMRC considers the error careless or deliberate, and coming forward yourself before HMRC identifies the issue generally results in a lower penalty than waiting.

Can HMRC change my tax return without telling me?

HMRC can make certain corrections within nine months of your filing date, but it will notify you of any change made. Anything beyond a simple correction, such as a discrepancy found through a compliance check, involves a more formal process where you’re kept informed and can respond.

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Articles Articles Blogs Self-Assessment Taxation Services

Self Assessment for First-Time Taxpayers: How to Register and File Your First Return

Filing a Self Assessment tax return for the first time can feel intimidating, mostly because nobody explains the process until you’re already up against a deadline. The good news is that once you understand the sequence — register, get your reference number, then file — it’s a manageable, one-time learning curve.

If you’d rather have someone check your registration and return before you submit, book a free 15-minute consultation with Felix Accountants — it’s a quick way to make sure your first return is right.

Who Needs to Register for Self Assessment?

You generally need to register if, in the tax year in question, you had income from self-employment over £1,000, rental income, foreign income, capital gains, dividends or savings above certain thresholds, or if you need to pay the High Income Child Benefit Charge. Self Assessment isn’t limited to the self-employed — many first-time filers are landlords, company directors, or people with a side income alongside employment.

The Registration Deadline

If you need to file for the first time, you must register with HMRC by 5 October following the end of the tax year in which the income arose. For example, if you started earning untaxed income at any point between 6 April 2025 and 5 April 2026 (the 2025/26 tax year), you need to register by 5 October 2026. Miss this and you can still register late, but you risk penalties if it causes you to miss the return deadline too.

How to Register: Step by Step

  1. Decide your category. HMRC’s registration route differs slightly depending on whether you’re self-employed, a landlord, a partner in a business, or none of the above but still need to file.
  2. Register online with HMRC. Use the appropriate GOV.UK registration service for your circumstances and set up a Government Gateway account or sign in with GOV.UK One Login.
  3. Receive your Unique Taxpayer Reference (UTR). HMRC posts this, usually within around 10 working days in the UK (longer if you’re abroad). You cannot file a return without it.
  4. Activate your online account. A separate activation code arrives by post, which you’ll need to complete sign-in for the online filing service.
  5. Set up your personal tax account. This is worth doing early — see our guide on how to set up your personal tax account for the details.

Filing Deadlines You Need to Know

DeadlineWhat it’s for
5 OctoberRegister for Self Assessment for the tax year just ended
31 OctoberPaper return deadline
31 January (following year)Online return deadline and balancing payment due

Our guide to the UK tax year and key dates covers how these deadlines fit into the wider tax calendar, including payments on account.

What Happens If You Miss the Deadline?

Missing the registration deadline alone doesn’t always trigger an automatic penalty, particularly if you don’t end up owing tax. Missing the filing deadline is different: HMRC applies an automatic £100 penalty even if you owe no tax, rising to daily penalties after three months. Full details are in our article on HMRC’s £100 fine for missing the tax deadline.

Common First-Time Filer Mistakes

  • Leaving registration until September or October and getting caught out by UTR postal delays
  • Not keeping records of income and expenses from day one, making the return far harder to complete accurately
  • Forgetting to declare all sources of income, not just the “main” one — for example, a small amount of rental income alongside employment
  • Assuming Self Assessment is only for the self-employed and missing the deadline as a first-time landlord
  • Not budgeting for payments on account, which can catch new filers by surprise in year two

Record-Keeping From the Start

Good record-keeping makes your first return far less stressful and gives you a solid foundation for every year after. Keep invoices, receipts, bank statements and any correspondence relevant to your income and expenses as you go, rather than trying to reconstruct a year’s activity in January.

How Felix Accountants Can Help

We help first-time filers register correctly, understand what they can and can’t claim, and get their first return submitted well ahead of the deadline — taking the guesswork out of a process that only gets easier the second time around.

Frequently Asked Questions

How long does it take to get a UTR number?

HMRC typically posts your Unique Taxpayer Reference within around 10 working days if you’re in the UK, or up to 21 working days if you’re abroad. It’s sensible to register well before the 5 October deadline to allow for this.

Do I need to register for Self Assessment if I’m already employed and pay tax through PAYE?

Yes, if you have additional untaxed income — such as self-employment earnings, rental income, or significant dividends — on top of your PAYE employment. Self Assessment and PAYE aren’t mutually exclusive.

What if I register late?

You can still register after 5 October, but if this causes you to also miss the filing deadline, you may face penalties. It’s best to register as soon as you realise you need to, rather than waiting.

Can I file my first return on paper instead of online?

Yes, but the paper deadline (31 October) is earlier than the online deadline (31 January), so most first-time filers find it easier to register for online filing.