Common Tax Mistakes Landlords Make

Not Declaring Rental Income at All

HMRC recovered a reported £107 million through the Let Property Campaign in 2024-25, its biggest year yet, at an average of about £14,000 per disclosure according to FOI figures in the trade press. HMRC cross-matches deposit protection schemes, Land Registry records and booking platform data, so accidental landlords rarely stay invisible. Registering for self assessment as a landlord is due by 5 October after the first tax year of letting.

If you are already behind, a voluntary disclosure through the campaign gives you 90 days to calculate and pay once HMRC acknowledges your notification, with penalties usually far below the up to 100% charged when HMRC finds you first. The lookback runs 4 years where reasonable care was taken, 6 years for carelessness, and up to 20 years where HMRC was never told at all.

Claiming the Whole Mortgage Payment

Capital repayments were never deductible, and since 2020 even the interest cannot be deducted from profit. It earns the finance cost credit at 20% instead. Copying the full monthly mortgage payment into the expenses box remains one of the most common errors on returns HMRC reviews, and it understates profit twice over.

Mixing Up Repairs and Improvements

A repair restores what was there; an improvement adds something new or better, and only the repair is deductible against rent. Replacing single glazing with modern double glazing counts as a repair because it is the current standard equivalent, while an extension or a first-time loft conversion is capital. Improvements are not wasted, they join the base cost and reduce the gain on sale, but claiming them against rental profit invites a compliance check.

Missing the 60-Day CGT Deadline

Selling a rental triggers its own return and payment on account within 60 days of completion, separate from the annual self assessment. The 60 day reporting deadline runs from completion, not exchange, and missing it costs £100 immediately with further penalties at six and twelve months plus interest. Sellers routinely learn about it from the penalty letter.

Treating a Retained Deposit as Free Money

A deposit is not income when taken, but any amount kept at the end of a tenancy for damage or arrears becomes property income at that point. The matching repair costs are deductible, so the net effect is often small, but leaving the retained amount off the return entirely is the mistake HMRC looks for when it samples deposit scheme data.

Ignoring Making Tax Digital

Landlords whose gross property and self-employment income passed £50,000 in 2024-25 have been inside MTD for Income Tax since 6 April 2026, with digital records and quarterly updates, and the first quarterly update fell due in early August 2026. Late submissions accrue points, and four points converts into a £200 penalty, although quarterly updates get a penalty holiday for 2026-27 itself. The threshold drops to £30,000 in April 2027, and the NRLA guidance on Making Tax Digital is a solid orientation for landlords not yet caught.

Assuming the 50/50 Spouse Split Is Optional

Married couples and civil partners are taxed half each on jointly owned property regardless of who banks the rent. Putting all the income on the lower earner without holding unequal shares as tenants in common, evidencing them, and filing Form 17 within 60 days of signing is not planning, it is misreporting.

Overlooking the Non-Resident Landlord Scheme

Once a landlord lives abroad, the letting agent, or the tenant where rent tops £100 a week, must deduct 20% tax from the rent and pay it to HMRC quarterly. An NRL1 application lets HMRC approve gross payment instead, but the income remains taxable through self assessment either way. Landlords who emigrate and tell nobody create a liability for their own agent.

Binning Records Too Early

Business records must be kept at least 5 years after the 31 January filing deadline for the year they relate to, and failing to keep adequate records carries a penalty of up to £3,000. Purchase completion statements and improvement invoices matter for even longer, since they set the CGT base cost decades later. The guidance on property records from LITRG sets out what to keep. A professionally prepared landlord self assessment catches most of the errors on this page before HMRC does.

Frequently Asked Questions

How does HMRC know about my rental income?

Deposit protection scheme records, Land Registry ownership data, letting agent returns, and since 2024 mandatory reporting by platforms such as Airbnb and Booking.com all feed HMRC risking systems. Nudge letters asking about property income are generated from those matches.

Do I need to declare rental income if I make no profit?

If gross rent exceeds the £1,000 property allowance, the income must go on a return even when expenses wipe out the profit. Declaring a loss also protects it, since carried-forward losses only exist if they were reported.

How far back can HMRC go for undeclared rent?

Four years where you took reasonable care, six years where you were careless, and up to twenty years where you never told HMRC about the income at all.