Written by the TaxTune Editorial Team · Reviewed by our qualified accountants · Updated for 2026
The quick answer The costliest landlord tax mistakes are getting the mortgage interest relief wrong, missing allowable expenses, confusing repairs with improvements, forgetting the 60 day capital gains rule on a sale, and keeping poor records. Each is avoidable with the right approach.

The mistakes that cost the most

  1. Mishandling mortgage interest. Interest is no longer a simple deduction. Instead you get a 20% tax credit on the finance costs, which changes the sums, especially for higher rate taxpayers.
  2. Missing allowable expenses. Letting agent fees, insurance, repairs, safety checks and some travel are all claimable and often overlooked.
  3. Confusing repairs with improvements. Repairs are usually deductible now, while improvements are capital and relieved against a future gain.
  4. Forgetting the 60 day rule. Selling a rental means reporting and paying capital gains tax within 60 days of completion.
  5. Poor records. Without clear records of rent and costs, the return is harder and claims are weaker.

Letting property and unsure of the tax?

The finance cost rules and capital gains deadlines catch landlords out every year. TaxTune handles your property tax, claims every cost, and keeps you ahead of the deadlines.

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Frequently asked questions

How is landlord mortgage interest taxed now?

You no longer deduct mortgage interest from rental profit. Instead you receive a 20% tax credit on the finance costs, which increases the tax for higher rate landlords compared with the old rules.

What expenses can landlords claim?

Letting agent fees, insurance, repairs and maintenance, safety certificates, ground rent and service charges, and some travel, among others. Improvements are capital rather than an expense.

What is the difference between a repair and an improvement?

A repair restores the property and is usually deductible against rental profit. An improvement enhances it and is capital, relieved against a future capital gain instead.

Do landlords have to report a sale within 60 days?

Yes. Selling a residential rental at a gain must be reported and the capital gains tax paid within 60 days of completion, separately from the annual tax return.

Do I need an accountant as a landlord?

Once you have the finance cost rules, allowable expenses and possible capital gains to handle, an accountant usually saves more than the fee and keeps you ahead of the deadlines.