Between Section 24 restricting mortgage interest relief, evolving Making Tax Digital requirements, and the sheer number of allowable expenses people either miss or misclaim, it's easy to end up paying more tax than you need to, or worse, triggering an HMRC query you didn't see coming. Here are five of the most common tax mistakes landlords make in the UK, and what to do instead.
1. Not Accounting for Section 24 Properly
This is one of the most common tax mistakes landlords make, and often the most expensive. Since mortgage interest relief for individually-owned rental properties was restricted, many landlords are still calculating their tax position as though full interest deductibility still applies. In reality, relief is now given as a basic-rate tax credit rather than a full deduction against rental income, which can push some landlords into paying tax on money that never actually reached their pocket as profit.
2. Missing Allowable Expenses
Landlords frequently under-claim, not over-claim. Letting agent fees, landlord insurance, accountancy fees, certain repair and maintenance costs, and service charges (for leasehold properties) are all commonly forgotten, either because they weren't tracked at the time or because the landlord wasn't sure they qualified.
3. Getting the Improvement vs Repair Distinction Wrong
This deserves its own mention because it trips up landlords constantly. HMRC draws a real distinction between a repair — restoring something to its previous condition, an allowable expense against rental income — and an improvement, making something better than it was before, generally treated as a capital cost only relevant when you eventually sell. Replacing a faulty boiler with a like-for-like model is generally treated as a repair. Replacing it with a significantly higher-spec model is more likely to be treated, at least partly, as an improvement.
4. Ignoring Making Tax Digital Requirements
Making Tax Digital is being extended to landlords with qualifying rental income above certain thresholds, requiring digital record-keeping and quarterly updates rather than a single annual return. Some landlords are still treating this as a future problem rather than something to prepare for now, which risks a rushed, error-prone transition when it becomes mandatory for their situation.
5. Not Planning for Capital Gains Tax Before Selling
Landlords often think about Capital Gains Tax for the first time only after they've agreed a sale price, at which point most of the planning opportunity has already gone. CGT on residential property disposals also carries specific reporting deadlines that are shorter than people expect, and missing them can mean a penalty on top of the tax itself.
The Common Thread
Every mistake on this list comes down to the same root cause: reacting to landlord tax rules after the fact instead of planning around them in advance. The rules governing rental property have changed substantially in recent years, and they're likely to keep shifting. A landlord who reviews their position annually, rather than only at tax return time, is in a far stronger position to avoid these common mistakes altogether.
Frequently Asked Questions
Miscalculating the impact of Section 24 mortgage interest relief restrictions is one of the most frequent and costly mistakes, since many landlords are still working from pre-restriction assumptions about how much relief they can claim.
Not in the way you may be used to. Mortgage interest for individually-owned rental properties is no longer deducted directly from rental income; instead, relief is given as a basic-rate tax credit, which can result in a different — often higher — tax outcome than a straightforward deduction would.
It depends on whether it's a like-for-like replacement (generally a repair, allowable against rental income) or a significant upgrade beyond the original standard (generally treated at least partly as a capital improvement). This is a common area of dispute with HMRC, so keeping evidence of the property's condition before and after matters.
MTD requirements apply once qualifying income exceeds set thresholds, which have been adjusted more than once, so it's worth checking your current position rather than assuming it doesn't apply to you yet.
Get specialist landlord tax support. Avoiding these mistakes gets much easier with a specialist who reviews your position proactively rather than once a year. Our Landlords & Property Investors service is built specifically around the issues covered in this article — from Section 24 planning to Capital Gains Tax advice ahead of a sale.
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