Work out the monthly payment and total cost of a UK mortgage in seconds. Use the inputs below for a repayment mortgage (capital + interest) or switch to interest-only. The calculator shows the full breakdown and lets you compare two mortgage scenarios side-by-side.

How a UK mortgage payment is calculated

For a repayment mortgage, your monthly payment is determined by three inputs: the loan amount, the interest rate, and the term. The formula compounds interest monthly so that by the end of the term the loan is fully repaid. As a rough check: at a 5% rate over 25 years, every £100,000 of borrowing costs roughly £585 per month and £75,500 in interest over the life of the loan.

For an interest-only mortgage, you pay only the interest each month — the capital is repaid in one lump at the end of the term, typically from a sale, investment, or savings vehicle you have alongside it. Common on buy-to-let; harder to get on a residential mortgage post- 2014 affordability rules.

What affects your real-world rate

• Loan-to-value (LTV). Lower LTVs (more deposit) get materially better rates. The biggest cliff is around 60% LTV; below that, rates flatten.
• Term length. Longer terms reduce the monthly payment but materially increase total interest. A 30-year vs 25-year term on £250k at 5% adds roughly £25,000 in extra interest paid.
• Fixed vs variable. Fixed gives certainty; variable can be cheaper short-term but stress-test for rate rises.
• Credit profile. Better scores unlock better deals at the same LTV.
• Product fees. Low-rate products often have higher arrangement fees. The calculator's "total cost" doesn't include fees — add the fee and re-run if it's significant.

Worked examples

• £200,000 at 4.5% over 25 years (repayment): £1,112 per month, total cost £333,500.
• £300,000 at 4.5% over 25 years (repayment): £1,668 per month, total cost £500,300.
• £300,000 at 4.5% over 30 years (repayment): £1,520 per month, total cost £547,200 — £148 less per month but £46,900 more total.
• £300,000 at 4.5% interest-only over 25 years: £1,125 per month, total interest £337,500, plus you still owe £300,000 at the end.

Stress-testing

UK lenders are required to test affordability against a higher rate than the pay rate — usually the pay rate plus 1 percentage point, or the lender's standard variable rate plus 1%, whichever is higher. That's the rate they use to decide if you can afford the loan. If you're applying close to your borrowing ceiling, run this calculator with your pay rate plus 1% to sanity-check that the higher monthly payment is still survivable.

Mortgage advice

This calculator is an illustration only. We are not authorised by the Financial Conduct Authority to give regulated mortgage advice. For advice on which mortgage product is right for you, your circumstances and your risk profile, speak to an FCA-regulated mortgage broker. You can check a firm's authorisation on the FCA register.

Calculation method last reviewed: 16 May 2026.