It is easy for rental income mistakes to build up quietly, especially where a property was let for a short period, a letting agent handled the day-to-day work, or a landlord assumed the tax position was already taken care of. When the issue is later picked up, many landlords are surprised to find that the penalty outcome is often driven not only by the tax unpaid, but by how the disclosure is handled.
This guide explains the most common Let Property Campaign mistakes that can increase penalties and what to do instead. It focuses on the points that HMRC expects in a disclosure, including making sure all undeclared income is included and providing figures that can be supported with records or reasonable workings.
Why mistakes matter under the Let Property Campaign?
Using the Let Property Campaign allows landlords to come forward voluntarily and correct past issues with rental income. However, this does not mean penalties are fixed or minimal in every case. The way a disclosure is prepared and presented can have a significant impact on the penalty outcome.
Penalties are not based only on how much tax was unpaid. They are influenced by the overall quality of the disclosure and how the issue is handled once it has been identified. This is why certain mistakes can lead to higher penalties, even where a landlord has chosen to disclose rather than wait to be contacted.
What penalties are based on
When penalties are considered, three broad factors are taken into account.
First, the reason the rental income was not declared correctly. This links back to behaviour. Errors caused by a lack of reasonable care are treated differently from cases where income was knowingly left out or actively hidden. More serious behaviour carries a higher penalty range.
Second, how complete and accurate the disclosure is. A disclosure that includes all relevant years, all properties, and figures that can be explained or supported is treated more favourably than one that omits years, understates income, or relies on unrealistic estimates.
Third, how the landlord engages once the issue is identified. Coming forward voluntarily, providing information promptly, and cooperating with any follow-up questions can reduce penalties. Delays, incomplete responses, or the need for HMRC to chase missing information can push penalties higher.
Taken together, these factors explain why two landlords with similar amounts of unpaid tax can end up with very different penalty outcomes.
Mistake 1: Disclosing the wrong numbers of years
A common Let Property Campaign mistake is assuming there is a “standard” disclosure period, often quoted as six years, and applying it without checking the facts. In practice, the right period depends on your own timeline and why the rental income was missed.
For many landlords, the disclosure will focus on recent years. For others, it may need to cover a longer period, particularly where HMRC had not been told about the letting at all, or where the issue carried on after the landlord became aware it needed fixing. The key point is that the disclosure should match what actually happened, year by year.
Why this matters
If you leave out years that should have been included, the disclosure may not fully settle the position. That can lead to follow-up questions, extra calculations, and a longer process than necessary. It can also weaken the overall quality of the disclosure, because HMRC may need to revisit work that could have been dealt with first time.
For example,
A landlord starts letting in 2014/15 and does not declare the income. They later realise (for example, because they start dealing with Self Assessment for other reasons) that the rent should be included. If they only disclose the most recent years without explaining the full timeline, HMRC may ask why earlier years were not included and whether the disclosure period needs to be widened.
Mistake 2: Not describing the behaviour accurately
A disclosure can become more complicated if the explanation given for why the rental income was missed does not quite match what happened in practice. This matters because penalties are linked to the behaviour behind the error, so HMRC will look at the facts and the timeline, not just the wording used in the disclosure.
What “careless” and “deliberate” mean in everyday terms
- Careless usually means the landlord did not take enough care to get things right, but there was no intention to underpay tax.
- Deliberate usually means the landlord understood the income should be declared but chose not to declare it.
The important point is that behaviour is judged by what the evidence shows, not by the label chosen.
How this issue arises in real life
This often happens where the situation changes over time.
For example, a landlord may genuinely not realise at the start that rental income needs to be reported. Later, they may become aware (perhaps after dealing with other tax matters, speaking to an adviser, or reading guidance) that the income should be included. If the position is not corrected after that point, HMRC may view the later years differently to the earlier years.
It can also happen where the same omission continues year after year with no clear explanation, or where the overall picture suggests the income was kept out of view. HMRC treats active steps to hide something as more serious than a simple error.
Why this can increase penalties
If the behaviour described in the disclosure does not fit the facts, HMRC may ask for clarification and the disclosure may need to be revisited. That can lead to:
- more years needing to be included,
- higher penalty ranges being considered, and
- extra work to redo calculations and resubmit figures.
It can also slow the process down, because HMRC will need more information to understand what happened and when.
For example,
A landlord does not report rental income for the first few years because they did not realise it needed to be declared. Later, they become aware that the rent should be included, but the income continues to be left out for subsequent years. Even if the early years were a genuine oversight, the later years may be looked at more critically because the landlord’s knowledge and actions changed over time.
How to avoid this mistake
The best approach is to explain the story clearly, year by year:
- when the letting started,
- when the landlord first became aware there was a reporting issue, and
- what steps were taken after that point.
Mistake 3: Misunderstanding how loss years are treated under the Let Property Campaign
A common area of confusion under the Let Property Campaign is how years with rental losses, or years where no tax is due, should be treated. Some landlords assume every year within a disclosure period must be included. Others assume loss years can simply be ignored altogether. HMRC’s guidance takes a more specific approach.
Under the Let Property Campaign, the disclosure is normally focused on years where rental income has resulted in tax being underpaid. If, after deducting allowable expenses, a year results in a rental loss so that no tax is due, HMRC’s guidance says that year does not need to be included in the disclosure figures.
However, loss years can still be relevant. Losses may be carried forward and set against rental profits in later years. For that reason, the calculations and records for loss years should be retained, even though the year itself is not included as part of the disclosure.
For example,
A landlord incurs high repair costs in the 2020/21 tax year, resulting in a rental loss. In later years, the property generates taxable rental profits. The loss year does not need to be included in the Let Property Campaign disclosure, but the loss calculations should be kept because they affect how the later profits are worked out.
Why this misunderstanding can cause problems
This mistake can cause issues in two different ways. Including loss years unnecessarily can make a disclosure more complex than it needs to be. More commonly, however, confusion about loss years leads landlords to lose track of how profits and losses interact across different years, resulting in incorrect figures for the years that do need to be disclosed.
How to avoid this mistake
Start by identifying the years where rental income led to unpaid tax. Those are the years that normally need to be included in the disclosure. Where earlier years resulted in losses, keep the calculations and supporting records so you can explain how later profits have been calculated if asked.
Mistake 4: Using unrealistic figures or unsupported expenses
Another mistake that can increase penalties is submitting figures that cannot be properly explained or supported. This often happens where records are incomplete and estimates are used, but the estimates are not reasonable or consistent with the facts.
HMRC recognises that older records may not always be available and allows landlords to make reasonable estimates where necessary. However, the expectation is that figures are based on what can be justified, not on assumptions designed to minimise tax. Inflated expenses, understated rental income, or rounded figures with no clear basis can all undermine the credibility of a disclosure.
This becomes a penalty issue because accuracy and quality of disclosure are relevant factors. If figures appear unrealistic, HMRC may ask for further evidence, challenge the calculations, or require them to be revised. Where figures have to be corrected after challenge, the disclosure is less likely to be treated as complete and accurate from the outset.
For example,
A landlord no longer has full records for early years and estimates expenses at a high level each year without supporting information. If bank statements or other evidence suggest lower costs, the figures may be challenged and revised. This can increase penalties even though the landlord came forward voluntarily.
How to avoid this mistake
Where estimates are needed, base them on available evidence such as bank statements, letting agent summaries, or typical costs for the type of property and period involved. Be consistent from year to year and be prepared to explain how the figures were arrived at. Clear workings and reasonable assumptions are usually viewed more favourably than aggressive estimates that cannot be supported.
Mistake 5: Forgetting properties, rooms or periods of letting
Another common mistake is failing to include all sources of rental income within the disclosure period. This does not just mean forgetting an entire property. It can also include overlooking short letting periods or informal arrangements that did, in fact, generate taxable rental income.
This often happens where:
- a property was only let for a short time between purchases or sales,
- a room was rented out informally to a lodger, friend or family member, or
- a property was let overseas and assumed to be outside UK tax.
From a disclosure perspective, leaving out any period where rent was received can make the disclosure incomplete. Even small or short-term amounts form part of the overall rental income history and should be included if they fall within the disclosure period.
This matters for penalties because omissions can suggest the disclosure was not thorough. If additional income comes to light later, it may lead to further questions and revisions, which can reduce the credit given for making a voluntary disclosure.
For example,
A landlord discloses rental income from a main buy-to-let property but forgets that a spare room was rented out for several months in an earlier year. Even though the amounts were small, that income should have been included. Discovering it later can weaken the disclosure and increase penalties.
How to avoid this mistake
Before finalising the disclosure, review the entire period carefully and list every property and letting arrangement, including short lets and informal arrangements. It is usually better to include an item and explain it than to leave it out and have to deal with questions later
Mistake 6: Assuming the Let Property Campaign
Some landlords come forward under the Let Property Campaign expecting that penalties will automatically be small. The campaign does give you a route to put things right voluntarily, but it is not an amnesty, and it does not set penalties at a fixed “discounted” level. You are still expected to calculate the tax, interest and any penalties that apply.
Although the penalties are different from “late Self-Assessment return” penalties
It also helps to be clear that the campaign penalty position is not the same as the automatic penalties people often associate with Self-Assessment returns.
Situation | How penalties are commonly worked out |
|---|---|
Late Self Assessment return or Late payment | Fixed and timed penalties can apply( for example an initial penalty, then daily penalties after a period, and further penalties later), plus late payment penalties and interest |
Let Property Campaign disclosure | Penalties are usually linked to the tax that should have been paid, and the percentage can vary depending on why the issue happened, whether you came forward before HMRC |
A practical point that is often missed: if HMRC has already issued tax returns for recent years and they are still outstanding, those years usually need to be dealt with through the normal return process rather than being bundled into the disclosure.
Why this misunderstanding can lead to worse outcomes
Where landlords assume penalties will be low “because it’s the campaign”, they can take a relaxed approach to the disclosure. That is where problems start: missing years, unclear explanations, or figures that are not properly supported. If HMRC later raises questions and the disclosure has to be revised, it can become harder to reach a smooth settlement, even if the underlying tax owed does not change.
For example,
A landlord discloses rental income but does not provide clear workings or a simple explanation of what went wrong. HMRC asks follow-up questions and the figures are reworked. The tax may end up the same, but the overall outcome can be less favourable because the disclosure was not “right first time”.
How to avoid this mistake
Treat the disclosure like a formal correction that needs to stand up to review. A complete, accurate disclosure, with clear workings and a straightforward explanation, is far more likely to keep the process efficient and help achieve the best available outcome within HMRC’s normal framework
Mistake 7:Delaying disclosure after becoming aware of the issue
A final mistake that can increase penalties is delaying action after becoming aware that rental income has not been declared correctly. In many cases, landlords realise there is a problem but postpone dealing with it, often because they are unsure what to do or hope the issue will resolve itself.
From a penalty perspective, timing matters. Coming forward promptly once an issue is identified is generally viewed more favourably than waiting. A delay can make it harder to argue that the behaviour was careless rather than deliberate, particularly if rental income continues to be received and not declared during that period.
HMRC draws an important line between:
- Unprompted disclosure: you tell HMRC about the issue before they contact you about it.
- Prompted disclosure: you only come forward after HMRC have written to you, started a check, or otherwise raised the issue.
In general, an unprompted disclosure is treated more favourably because you are putting things right voluntarily. Leaving it too long can also make your position harder, especially if rental income continues to be received and nothing is done to correct the tax position during that time. The longer a problem continues, the harder it can be to explain it as a simple oversight.
How the penalty ranges can differ (prompted vs unprompted)
The table below shows the standard penalty ranges HMRC use for errors (inaccuracies). The key point is that the minimum penalty is usually lower if the disclosure is unprompted.
Behaviour | Unprompted disclosure | Prompted disclosure |
|---|---|---|
Careless | 0% to 30% | 15% to 30% |
Deliberate | 20% to 70% | 35% to 70% |
Deliberate and concealed | 30% to 100% | 50% to 100% |
Delays can also affect how cooperation is viewed. If a disclosure is only made after a long period of inaction, or after records have deteriorated further, this can reduce the credit given for taking responsibility and helping to resolve the issue.
For example,
A landlord realises in 2022 that rental income from earlier years was not declared, but takes no action and continues to receive rent without correcting the position. The disclosure is eventually made several years later. Even if the original omission was careless, the continued delay can make the overall behaviour look more serious and lead to higher penalties.
How to avoid this mistake
Once you become aware that rental income has not been declared correctly, it is usually best to take steps to address it without unnecessary delay. Even if figures cannot be finalised immediately, notifying HMRC and beginning the disclosure process helps demonstrate cooperation and can support a more favourable penalty outcome.
Worked example: same tax due, different penalties
To show why these mistakes matter, it helps to look at a simple hypothetical example. The figures below are illustrative only. Actual penalties depend on the facts of the case and HMRC’s assessment, but the example reflects how the rules operate in practice.
The starting point
Two landlords each have £20,000 of undeclared rental profits over several years. At a basic rate of tax, the tax underpaid is £4,000 in both cases.
The tax position is identical. What differs is how the disclosure is handled.
Scenario A: Careful and complete disclosure
- The landlord realises rental income was missed and acts promptly.
- The correct number of years is disclosed.
- All properties and periods of letting are included.
- Figures are supported by records or reasonable estimates.
- The behaviour is accurately described as careless.
In this scenario, the disclosure is unprompted, complete and cooperative. The penalty percentage applied may fall towards the lower end of the range for careless behaviour.
Illustrative outcome
- Tax underpaid: £4,000
- Penalty at 10% (illustrative): £400
- Interest charged separately
Scenario B: Incomplete disclosure with mistakes
- The landlord discloses only six years when the facts point to a longer period.
- Years with losses are left out.
- Some rental income is omitted initially and added later after questions are raised.
- Behaviour is described as careless, but the facts suggest later deliberate behaviour.
Although the same tax is ultimately paid, the disclosure has to be corrected and recalculated. This affects how cooperation and accuracy are viewed.
Illustrative outcome
- Tax underpaid: £4,000
- Penalty at 35% (illustrative): £1,400
- Interest charged separately
What this example shows
The tax underpaid has not changed. What has changed is:
- the accuracy of the disclosure,
- how behaviour is classified, and
- how cooperative the process appears.
These factors directly influence the penalty percentage. Multiple small mistakes can combine to produce a much higher penalty than expected.
Summary
Using the Let Property Campaign can help landlords bring undeclared rental income up to date, but the way a disclosure is handled has a direct impact on penalties. Penalties are not based only on the amount of tax underpaid. They are influenced by behaviour, the completeness and accuracy of the disclosure, and how promptly and cooperatively the issue is addressed.
The most common mistakes that increase penalties include disclosing the wrong number of years, misdescribing behaviour, leaving out years with losses or no tax to pay, using unsupported figures, and delaying action after becoming aware of an issue. These mistakes can combine to produce a much higher penalty, even where the tax itself does not change.
A careful, honest and complete disclosure from the outset is usually the best way to minimise penalties and bring matters to a proper conclusion. Understanding where landlords commonly go wrong helps avoid unnecessary costs and reduces the risk of further questions or delays.
Need Help?
Need more expert advice on how to avoid common Let Property Campaign mistakes?
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