Section 24 mortgage interest calculator
See what the loss of full mortgage interest relief actually costs you as a landlord, compared with the old rules.
Your Section 24 cost
Change the numbers, the results update instantly.
Assumes you're a UK individual landlord, not a limited company. Always take advice before acting.
How it works
Since Section 24 took full effect, individual landlords can no longer deduct mortgage interest from rental income before working out tax. Instead, rental profit is taxed on income minus allowable costs only, with mortgage interest excluded, then a flat 20% tax credit is applied against the tax bill for the interest paid. Under the old rules, interest was simply deducted like any other cost before tax was calculated, which was more generous for higher-rate taxpayers. This is one of the biggest tax changes affecting landlords and property investors today.
Frequently asked questions
Why does Section 24 cost more for higher-rate taxpayers?
The replacement 20% tax credit is worth less than a full deduction to anyone paying tax above the basic rate, since the deduction used to be relieved at their marginal rate, not capped at 20%.
Does this apply to limited company landlords?
No, companies holding property deduct mortgage interest as a normal expense against corporation tax and are not affected by Section 24, which only applies to individual landlords.
Can Section 24 push me into a higher tax band?
Yes, because rental profit is now calculated before deducting interest, your taxable income for band purposes can be higher than your real cash profit, sometimes pushing you into the higher rate band or even affecting the personal allowance taper.
Is incorporating my portfolio a way around this?
It can be for some landlords, but incorporation has its own tax costs and implications. We work through this regularly with our landlord and property clients, book a free call to talk through whether it makes sense for your portfolio.
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These results are a simplified illustration based on 2026/27 rates, not advice. Your real position depends on your full circumstances. For a personalised answer, book a free consultation.
Numbers looking complicated?
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