Mortgage Repayment Calculator

Enter the remaining mortgage amount, the annual interest rate, and how many years and months are left to see the level monthly repayment. Add an optional yearly overpayment to see how much sooner the balance would be cleared. Use Swap — or the Time remaining tab — to turn that around and enter a monthly payment instead, to see how long it would take to clear the balance.

How the calculations work

This is a standard repayment mortgage estimate: each monthly payment covers that month's interest and some of the remaining amount. Interest is applied monthly as the annual rate divided by 12.

Monthly payment uses the usual repayment formula: remaining amount × [r(1 + r)ⁿ] ÷ [(1 + r)ⁿ − 1], where r is the monthly interest rate and n is the number of months left. If the interest rate is 0%, the remaining amount is split evenly across those months.

Time remaining rearranges the same formula to find n from a monthly payment. If the payment does not cover the first month's interest, the remaining amount would never be repaid.

A yearly overpayment is an extra amount paid once a year, on top of the monthly repayment, at the end of every 12th month. It does not change the calculated monthly payment. It does reduce the remaining amount sooner, so the mortgage is usually cleared earlier and less interest is paid. If the remaining balance is smaller than that year's overpayment, only the amount still owed is used.

The remaining balance chart plots the outstanding amount at the start and at the end of each year, down to zero. If you enter a yearly overpayment, a dashed line shows the same monthly payment without those extra payments.

Figures are rounded to the nearest penny. The last payment can be slightly smaller than the regular monthly amount. The estimate assumes the interest rate stays the same and you make every payment on time, with no fees, payment holidays, or product switches.