Mortgage Repayment Calculator: Monthly Payment, Total Interest, Full Term

How repayments are calculated

A repayment mortgage uses the standard amortisation formula: the monthly payment is set so that, at your interest rate, the loan reaches exactly zero at the end of the term. Early payments are mostly interest; later payments are mostly capital. This calculator applies that formula directly: M = L·r / (1 − (1+r)⁻ⁿ) with monthly rate r and n monthly payments, which is why its output matches the shape of any lender's quote even though it isn't one.

Worked example: borrow £225,000 (a £250,000 home with a £25,000 deposit) at 4.5% over 25 years and the repayment is about £1,251 a month, roughly £375,000 repaid in total, of which about £150,000 is interest.

Repayment vs interest-only

Interest-only looks cheaper because it is paying for less: the monthly cost covers only the interest, and the entire loan is still owed at the end of the term. It has legitimate uses (some landlords, bridging situations, strong repayment vehicles) but for most owner-occupiers the repayment basis is the realistic planning number. The calculator shows both, with the loan left at term end made explicit.

What moves your payment

Three levers: the rate (each percentage point matters more than any other input), the term (longer is cheaper monthly, dearer in total), and overpayments (which shorten the term from the inside). This page is arithmetic, not advice. It can't predict rates or tell you which product to pick, and we are not a lender or broker.

The repayment is only the recurring cost

Buying has one-off costs on top of the deposit: stamp duty, conveyancing, survey and search fees, and owning has recurring lines beyond the mortgage: council tax, energy, insurance, and service charge on leasehold flats. The true cost of owning calculator stacks those into one monthly figure.