Let Property Campaign Penalty Calculator: Tax, Penalty Band & Look-Back
Undeclared rental income? Estimate the tax, HMRC's penalty band (0% to 100% of the tax) and how many years it can go back — from HMRC's own tables.
Embed this calculator on your website — free, no sign-up, always on the current rates. Paste the code below; the widget links back to this page so your visitors can read the full guide.
<iframe src="https://landlordtaxlab.co.uk/embed/let-property-campaign-penalty-calculator" title="Let Property Campaign Penalty Calculator — landlordtaxlab.co.uk" width="100%" height="760" style="border:0;max-width:960px" loading="lazy"></iframe>
Terms: keep the “Powered by” link intact; rates come from our data, updated when HMRC changes them; general information, not advice.
The Let Property Campaign is HMRC’s standing route for landlords to declare rental income they have not told HMRC about — on better terms than waiting to be caught. The cost of coming forward has three parts: the tax itself for the years HMRC can assess, a penalty expressed as a percentage of that tax, and interest. This estimator uses HMRC’s own penalty table for a “failure to notify” (factsheet CC/FS11) and its own look-back rules to give you a realistic range before you speak to an adviser.
How far back HMRC can go
HMRC’s Let Property Campaign guide sets the limits by behaviour: if you took reasonable care but still underpaid, 4 years; if you were careless, 6 years; if the underpayment was deliberate — or you never registered for Self Assessment at all — 20 years. Most landlords who simply never registered fall into the 20-year bracket on the registration point even where the behaviour was careless, which is why the estimator defaults the “years assessed” to the behaviour you select rather than the years you type.
The penalty table HMRC uses
| Behaviour | Unprompted | Prompted |
|---|---|---|
| Non-deliberate, disclosed within 12 months of the tax being due | 0% to 30% | 10% to 30% |
| Non-deliberate, disclosed more than 12 months after | 10% to 30% | 20% to 30% |
| Deliberate | 20% to 70% | 35% to 70% |
| Deliberate and concealed | 30% to 100% | 50% to 100% |
“Prompted” means HMRC had already contacted you — a nudge letter, a compliance check, or a data-matching letter about Land Registry, letting-agent or deposit-scheme records — before you disclosed. Where in the band you land depends on how fully you tell HMRC, help it quantify the tax, and give access to records; a complete, cooperative disclosure earns the bottom of the range.
What the estimator does not include
- Interest on the late tax for every year, at HMRC’s late-payment rate for the period — often the second-largest number. Ask an adviser to run it year by year.
- Class 2 / Class 4 National Insurance — not due on ordinary rental income, so usually nil.
- Any reduction for a “reasonable excuse”, which can take a non-deliberate penalty to zero.
- Higher penalties for offshore matters, which have their own regime.
The process, in HMRC’s words
You notify HMRC that you intend to disclose, then have 90 days to calculate and pay what you owe, using the disclosure form. You can pay in instalments if you cannot pay in full — agree that before the deadline, not after. Once accepted, HMRC issues a letter confirming the disclosure has been dealt with; the years disclosed cannot then be reopened unless new facts emerge.
Before you start
Rebuild each year’s figures properly: rent received, then every allowable expense, with the mortgage-interest rules of that year (full deduction before 2017/18, tapering to the 20% credit from 2020/21). Many landlords who disclose find the tax is smaller than they feared once expenses are claimed. Where a property was jointly owned, each owner discloses their share — see joint ownership and Form 17.
Penalty percentages and look-back limits quoted from HMRC’s Let Property Campaign guide and factsheet CC/FS11, re-read 4 September 2026 (research/2026-09-04/LTL-FACTS-PACK.md). General information, not advice — a disclosure is worth doing with an adviser who handles them regularly.
Asked constantly
Data matching: Land Registry ownership records, tenancy-deposit scheme registrations, letting-agent returns, council tax and housing-benefit records, and mortgage data. A nudge letter based on that data makes any later disclosure a prompted one, which raises the minimum penalty.
Yes. Unlike time-limited campaigns, HMRC has kept the Let Property Campaign open since 2013 with no announced closing date. Check the gov.uk guide for any change before you rely on it.
HMRC's stated policy is to use criminal investigation only in the most serious cases, and a full voluntary disclosure weighs heavily against it. Deliberate concealment is where the risk sits; a careless failure to register almost never goes that way.
That is the choice that turns careless into deliberate if HMRC later matches the data. Disclosing the back years yourself, before any letter, keeps you in the unprompted band — the cheapest place in the table.
Doing this every quarter, not just once?
Keep the same figures all year instead of re-typing them: rent and expenses per property, the Section 24 finance costs and the MTD quarterly totals, in one workbook.
Landlord Tax Lab stays free. We also sell the Landlord Tax Pack: one Excel workbook for up to 10 properties that logs rent and expenses per property, maps every line to its SA105 box, keeps Section 24 finance costs out of the expense boxes, and rolls up the MTD quarterly totals. £19 once — no subscription.
Disclosure: we make and sell the Tax Pack — this is our own product, not a paid recommendation. It does not file anything with HMRC and it is not tax advice; filing goes through you, your accountant or software on HMRC’s compatible-software list.
Sources
The primary documents this page is built from. Links checked 5 September 2026.
- Let Property Campaign: your guide to making a disclosure — GOV.UK / HMRC
- Let Property Campaign: examples of tax errors landlords make — GOV.UK / HMRC
- Self Assessment tax returns: penalties — GOV.UK