Mortgage Repayment Calculator UK

How your mortgage repayment is worked out

A repayment mortgage, also called capital and interest, uses the standard amortisation formula. Each monthly payment covers the interest charged on the balance for that month, and whatever is left over reduces the capital. Because the balance shrinks over time, the interest portion of each payment falls and the capital portion rises. The formula that ties it together is payment = P × r ÷ (1 − (1 + r)⁻ⁿ), where P is the amount borrowed, r is the monthly interest rate, and n is the total number of payments. This mortgage payment calculator applies it for monthly, fortnightly and weekly payments.

Loan amount or property price and deposit

You can enter the amount you are borrowing straight into the calculator, or switch to property price and deposit and let it work out the loan for you. Entering a price and deposit also shows your loan to value, or LTV, which is the loan as a percentage of the property price. LTV matters because lenders price their deals in bands: a bigger deposit drops you into a lower LTV band, which usually means a lower interest rate and a smaller monthly payment.

Repayment vs interest-only

A repayment mortgage clears both the interest and the capital, so the balance reaches zero and you own the home at the end of the term. An interest-only mortgage covers just the interest, so the monthly payment is lower but the full amount borrowed is still owed when the term ends and has to be repaid another way. Interest-only lending is now mostly limited to buy-to-let and some later-life products. Toggle between the two above to see the gap for your own mortgage.

A worked example

Take a £250,000 mortgage at 4.5% over 25 years, paid monthly. The monthly rate is 4.5% ÷ 12 = 0.375%, over 300 payments, which gives a payment of about £1,390 a month. Across the full term that adds up to roughly £416,700 repaid, of which around £166,700 is interest. Shorten the term or lower the rate and the total interest drops sharply, which is why the term and rate matter as much as the amount you borrow.

Using it as a remortgage calculator

When a fixed deal ends you usually roll onto the lender’s standard variable rate, which is often higher, so many people remortgage to a new deal to keep the payment down. To use this as a remortgage calculator, enter your outstanding balance as the loan amount and the remaining years as the term, then run it once at your current or SVR rate and again at the new deal’s rate. On a £250,000 balance over 25 years, moving from a 7% SVR to a 4.5% fix drops the monthly payment from about £1,767 to roughly £1,390, a saving of around £377 a month. Weigh any product or exit fees against that saving before you switch.

What the calculator leaves out

This is a clean estimate of the payment on the amount borrowed. It assumes a single rate for the whole term, so it does not model the jump from a fixed deal onto a standard variable rate, or a later remortgage. It also excludes arrangement fees, valuation and legal costs, buildings insurance and any product fee added to the loan. Treat the figure as the core monthly payment and add those separately.

Frequently asked questions