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UK Mortgage Calculator

Free UK mortgage calculator. Compute monthly repayment, total interest, and amortisation for any fixed-rate mortgage.

Published

UK repayment mortgage payment.

Monthly payment

Total interest

Total paid

Your breakdown

Updates live as you type
Item Amount

Worked example

Take a £250,000 repayment mortgage at a 5 percent annual rate over a 25-year term. The monthly rate is 5 percent divided by 12, and there are 300 monthly payments. Feeding those into the standard repayment formula gives a monthly payment of £1,461. Over the full 300 months you pay £438,443 in total, so the interest cost is £188,443, which is almost as much again as the amount borrowed. That is why even a small cut in rate or a shorter term changes the total dramatically.

How it is calculated

A repayment mortgage uses the standard amortising formula, where the monthly payment is principal times the monthly rate, multiplied by (1 plus the monthly rate) raised to the number of payments, divided by that same compounded factor minus one. The monthly rate is the annual rate divided by 12, and the number of payments is the term in years times 12. Early on most of each payment is interest because the balance is large, and the principal share grows every month as the balance falls. Multiplying the monthly payment by the number of payments gives the total repaid, and subtracting the original loan leaves the total interest. The calculation assumes a fixed rate for the whole term, so real-world reversion rates after a fixed deal will change the figures.

Frequently asked questions

Repayment vs interest-only?
Repayment mortgages pay down principal each month, eventually clearing the loan. Interest-only pay only the interest with principal unchanged, requiring a separate repayment plan at term-end (typical for BTL).
What is the standard UK mortgage term?
Most UK residential mortgages run for 25 years, though lenders now offer terms up to 35 or even 40 years to keep monthly payments affordable. A longer term reduces the monthly payment but substantially increases total interest paid over the life of the loan.
How does overpaying affect my mortgage?
Making overpayments reduces the outstanding balance, which cuts the interest charged each month and shortens the overall term. Many lenders allow overpayments of up to 10 percent of the balance per year without early repayment charges, so check your mortgage terms before making large lump-sum payments.
Does this calculator account for rate changes after a fixed-rate deal?
No, this calculator assumes a single fixed rate for the entire term. Most UK borrowers take a 2 or 5 year fixed deal and then revert to the lender's standard variable rate or remortgage to a new deal. When your fixed period ends, recalculate with the new rate and the remaining balance to get updated figures.

Related calculators

Sources

  1. HMRC — Income Tax Rates and Personal Allowances 2026/27, HM Revenue & Customs
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