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Section 24 Calculator

See how much extra tax the mortgage-interest restriction costs you — the difference between today’s rules and the old full-deduction treatment.

Salary, pension etc. — sets your tax band.

Enter your rent and mortgage interest to see the Section 24 impact.

Based on 2026/27 UK tax rules · GOV.UK source · This is an estimate, not personal tax advice — always check your own circumstances with HMRC or a qualified accountant.

What Section 24 changed

Until 2017, landlords deducted mortgage interest from rental income before working out tax. Section 24 phased that out. Since 2020/21 you add back the full interest and instead receive a 20% tax credit on it. If you’re a basic-rate taxpayer, 20% relief and a deduction come to the same thing. If you’re a higher-rate taxpayer, you lose the difference between your marginal rate and 20% — which can be substantial on a large mortgage.

This calculator shows both treatments side by side so you can see the real cost. To estimate your overall rental tax, use the rental income tax calculator.

Common questions

What is Section 24?
Section 24 is the change that stopped residential landlords deducting mortgage and other finance costs from their rental income. Fully in force since 2020/21, it replaces the deduction with a basic-rate (20%) tax credit.
Who does Section 24 affect most?
Higher- and additional-rate taxpayers with mortgaged buy-to-lets. Because relief is capped at 20% rather than your marginal rate, you effectively pay tax on income used to service the mortgage. Basic-rate taxpayers are largely unaffected.
Can I avoid Section 24 by using a limited company?
Companies aren’t subject to Section 24 and can deduct interest, but incorporating has its own costs and tax consequences (SDLT, CGT, mortgage rates, profit extraction). It’s a complex decision — take qualified advice before acting.

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