Let Property Campaign: Know the Years You Need to Declare
If you’re a landlord who has discovered that rental income wasn’t reported correctly to HMRC, the first question is rarely “how much tax do I owe?” It’s “how far back does this go?”
That question trips up more landlords than almost any other part of the Let Property Campaign. There’s no single, universal answer — HMRC doesn’t apply a flat six-year rule to everyone. Instead, the number of tax years you’re required to disclose depends on why the income went unreported in the first place. Get that wrong, and you risk an incomplete disclosure, a challenge from HMRC, and additional penalties further down the line.
This guide walks through exactly how the look-back period is calculated, how HMRC’s three behaviour categories work, and the mistakes that most commonly catch landlords out.
Not sure where your disclosure should start? Book a free, no-obligation discovery call with our Let Property Campaign specialists and we’ll help you work out exactly which years apply to your situation.
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Who the Let Property Campaign Is For
The Let Property Campaign is HMRC’s voluntary disclosure route for landlords whose rental income hasn’t been reported correctly — whether that’s income left off a return entirely, or a return filed with the wrong figures.
It’s built around individual landlords rather than corporate structures, and it covers a wide range of situations:
- Landlords with a single rental property who never registered for Self Assessment
- Portfolio landlords who missed one property among several
- UK residents letting property overseas, and overseas residents letting UK property
- Short-term lets that were sold before the income was ever declared
- Landlords already in Self Assessment whose figures were wrong
There’s no minimum threshold. HMRC’s own guidance treats the campaign as open to anyone with undeclared or under-declared rental income, regardless of how small the sums involved. For a broader look at how UK rental income is taxed in the first place, our property tax guide covers the basics landlords are expected to know.
What the Campaign Does — and Doesn’t — Change
It’s worth being clear-eyed about what the Let Property Campaign actually offers.
It gives you a structured way to:
- Come forward before HMRC finds the issue independently
- Calculate and settle tax, interest, and penalties yourself, with HMRC’s oversight
- Generally receive more favourable treatment than if HMRC uncovers the problem through a compliance check
It does not:
- Cap or reduce HMRC’s legal power to assess tax
- Let you pick a convenient disclosure period
- Guarantee lower penalties automatically — that still depends on how the disclosure is made and how complete it is
In short, coming forward voluntarily is the advantage. The scope of what you need to disclose is still governed entirely by HMRC’s rules, not by your preference.
Why “Behaviour” Is the Deciding Factor
Here’s the part that catches people out: the number of years you must go back is not fixed. It’s determined by HMRC’s assessment of why the tax went unpaid — referred to as your “behaviour.”
This matters for a legal reason, not just a moral one. The standard assessment window is limited, but HMRC can extend it — to six years or even twenty — only where specific statutory conditions are met. Those conditions hinge on whether the loss of tax resulted from carelessness or from a deliberate decision not to declare.
Get the behaviour classification wrong on your disclosure, and HMRC can challenge it later — reopening a case you thought was closed.
Careless behaviour → normally up to 6 tax years
This applies where reasonable care wasn’t taken, but there was no intent to avoid tax. Typical examples include:
- Not realising rental income needed declaring at all
- Misapplying the rules on allowable expenses
- Errors on a return that went unchecked
HMRC assesses “reasonable care” against what a sensible, prudent person in the landlord’s position would have done. Using an accountant is actually meaningful evidence here — it can support the argument that reasonable care was taken, even if a mistake still occurred.
Example: A landlord claims expenses that turn out not to be allowable, purely from misunderstanding the rules, and it’s picked up years later. This typically results in a six-year disclosure.
Deliberate behaviour → up to 20 tax years
This is where rental income was left out knowingly — not through misunderstanding, but by choice. Examples include:
- Receiving rent and simply not declaring it
- Knowing tax registration was required and not doing it
- Repeated, ongoing omission of rental income from returns
Example: A landlord has let a property since 2010 and knowingly never registered for tax on the income. Because the letting activity — and the unpaid tax — started in 2010/11, that’s where the disclosure begins, not an arbitrary twenty years prior.
Deliberate and concealed behaviour → up to 20 tax years, with heavier penalties
The most serious category applies where income wasn’t just omitted, but active steps were taken to hide it — for example, rent paid into an account not linked to the landlord’s name, no records kept at all, or misleading information given if questioned. The look-back period mirrors deliberate behaviour, but penalties sit at the top end of the scale.
How Behaviour Affects Penalties and Interest
Behaviour doesn’t only decide how far back you go — it drives the penalty range too. Careless errors sit at the lower end; deliberate and concealed behaviour at the top. On top of any penalty, interest accrues separately on the unpaid tax from the original due date until it’s settled, regardless of category.
This is why correctly identifying — and being able to justify — your behaviour category matters as much as the arithmetic. Landlords weighing up how to minimise the overall cost of a disclosure may also find it useful to look at our guide to tax-saving strategies for legitimate ways to manage the ongoing liability once matters are up to date.
Working Out Which Years Actually Belong in Your Disclosure
Once you know your behaviour category, the next step is translating that into an actual list of tax years. This isn’t a matter of picking a convenient starting point — it follows a specific logic.
1. Start with the most recent tax year. If a return is already due for the latest year, that’s usually handled through normal Self Assessment rather than folded into the historic disclosure — the Let Property Campaign is then used to correct everything before it.
2. Count backwards using your behaviour category. Up to six years for careless behaviour, up to twenty for deliberate or concealed behaviour — but only as far as there was genuine letting activity and unpaid tax. If the property wasn’t let, or there was no under-declared income, in an earlier year, that year simply isn’t part of the disclosure.
3. Confirm each year actually generated a tax liability. More on this below — not every year within the look-back window needs to be included.
Careless example: An error identified in 2025 typically means reviewing 2019/20 through 2024/25 — the six most recent tax years — and including only the ones with genuine underpaid tax.
Deliberate example: Letting began in 2010/11 and income was knowingly withheld. Because that’s when the tax loss started, the disclosure runs from 2010/11 forward — not from an earlier, arbitrary date.
When Your Behaviour Isn’t Consistent Throughout
It’s common for a landlord’s situation to shift over time — genuine confusion in the early years, followed later by a conscious decision not to declare once the rules became clear.
Where that happens, HMRC applies the most serious behaviour identified across the whole period when deciding how far back it can assess. A change from careless to deliberate partway through can therefore extend the maximum look-back significantly — even though the earliest years were a genuine mistake.
Example: A landlord starts letting in 2014/15 and doesn’t realise the income is taxable until 2018/19, from which point they’re aware but continue not declaring. The later deliberate conduct means HMRC can, in principle, assess up to twenty years — but because letting only began in 2014/15, that’s still the actual start of the disclosure.
Do You Have to Include Years With No Tax Due?
Not automatically. If, after allowable expenses, a year produced a loss rather than a profit, HMRC’s guidance says that year doesn’t need to be included in the disclosure figures — because no tax was underpaid.
That doesn’t mean loss years are irrelevant, though. Rental losses can be carried forward against future profits, so it’s worth keeping the calculations and supporting evidence for those years even if they’re excluded from the disclosure itself.
Low rental income is a different matter from a loss. If a year generated modest income but tax was still underpaid, that year belongs in the disclosure — the test is whether tax was due, not how much income there was.
Missing or Incomplete Records
Gaps in your paperwork are common, especially for lettings going back a decade or more — and they don’t remove the obligation to disclose. HMRC expects a reasonable, honestly reconstructed estimate rather than perfect records.
In practice, that usually means piecing figures together from:
- Bank statements showing rental receipts and related payments
- Letting agent statements or tenancy agreements
- Surviving invoices, or realistic estimates based on the type of property and period involved
The estimate needs to be consistent and defensible — inflating costs or understating income to fill gaps undermines the whole disclosure. Where records genuinely don’t exist, say so plainly as part of the submission; HMRC’s guidance acknowledges this happens and expects a fair attempt, not certainty.
Mistakes Landlords Commonly Make With Disclosure Years
Most problems with Let Property Campaign disclosures come down to a handful of recurring errors:
- Assuming a flat six-year rule applies to everyone, regardless of behaviour
- Excluding a low-income year that still owed tax, confusing “small” with “no liability”
- Understating earlier behaviour as careless when it later became deliberate, risking a challenge and an extended look-back
- Overlooking a whole property or letting period — a short let, an informally rented room, or overseas income that got missed
- Delaying the disclosure because records are incomplete, when a reasonable estimate would have been accepted
Each of these can slow the process down or trigger further HMRC questions, so it’s worth getting the classification and the years right before you submit rather than after.
Frequently Asked Questions
Does HMRC always go back six years? No. Six years applies to careless behaviour. Deliberate or concealed behaviour can extend the look-back to twenty years.
Can I leave out a year because I don’t have full records? No — missing records don’t remove the obligation to disclose. A reasonable, well-explained estimate is expected instead.
Do I need to include a year where the property made a loss? Generally no, if no tax was actually due for that year. Keep the figures anyway, since losses can carry forward.
What if my reason for not declaring changed over time? HMRC applies the most serious behaviour identified across the whole period, which can extend the maximum assessable years even if the issue started as a genuine mistake.
Getting Local, Specialist Help
Because the correct disclosure period depends so heavily on the specific facts of your case, generic guidance can only take you so far. Our Let Property Campaign specialists work with landlords across the UK, including in:
Summary
The number of years you need to disclose under the Let Property Campaign comes down to why the income wasn’t declared correctly — not a fixed rule. Careless errors typically mean a six-year look-back; knowingly withheld income can extend that to twenty. Within that window, only years with genuine letting activity and underpaid tax need to be included, and incomplete records are addressed with reasonable estimates rather than used as a reason to delay.
Getting the years — and the behaviour classification behind them — right the first time is what keeps a disclosure from being challenged or extended later.
Ready to find out exactly which years apply to you?