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What happens when my buy to let fix ends?

Put in the loan, the rate you pay now and the rate you expect next. This shows the change in cash flow, where it breaks even, and whether the rent still passes a lender's test for the loan you have.

Your mortgage
£
years
Only used for a repayment mortgage.
%
%
A broker can tell you what is available now for your loan to value.
The property
£
£
Agent fee, maintenance, insurance, service charge and compliance, averaged over the year.
£
Lender test
%
%

How this is calculated

The monthly payment is worked out at both rates: interest only is the loan times the rate divided by twelve, repayment uses the standard annuity formula over the years left.

Cash flow is rent less the monthly running costs and the mortgage payment. The break-even rent covers the running costs and the payment at the new rate. The break-even rate is the rate at which the payment uses up everything the rent leaves after costs.

A lender refinancing the loan applies two limits: loan to value, and rental cover, which divides the annual rent by the test rate and by the cover required. If the lower of the two is below what you owe, the shortfall is shown.

Rates and assumptions used

Common rental cover, basic rate or company125%
Common rental cover, higher rate145%
Common test ratearound 5.5%, varies by lender

Statutory rates last checked July 2026. Source: HMRC and gov.uk.

Worked example

A £150,000 interest-only loan moving from 2.5% to 5.5% raises the payment from £313 to £688 a month. With £1,100 rent and £250 of monthly running costs, cash flow falls from £538 to £163 a month, and it reaches zero at a rate of 6.8%. At 125% cover tested at 5.5%, the rent supports a loan of £192,000, so a new lender would still refinance it.

Common questions

Do I have to pass the rental cover test again?

Usually not if you take a new product from your existing lender without borrowing more, often called a product transfer. Moving to a new lender, or borrowing more, normally means passing the new lender's test.

What can I do if the numbers no longer work?

Options include a longer fix, switching to interest only, raising the rent where the tenancy allows, paying down part of the loan, or selling. A mortgage broker can compare lenders whose tests suit your situation.

Does this include tax?

No. For individual landlords, a higher mortgage payment does not reduce the tax bill pound for pound, because only a 20% credit is given on mortgage interest. Use the Section 24 calculator to see the tax side.

This is an estimate, not financial advice. The result is arithmetic based on the figures you entered and the published rates listed above. Tax on rental profit is not included. Lenders apply their own criteria and will reach different figures. For advice specific to you, speak to a qualified adviser or mortgage broker.
Work out next

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Tax on rental profit with the 20% interest credit, compared with owning through a company.

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Cash flow, yield, return on cash, a rate stress test and a projection with IRR.