Buy a home · UK
Mortgage Overpayment Calculator
See what overpaying your mortgage could save you. Add a monthly overpayment or a one-off lump sum to find out how much interest you cut and how many years you knock off the term.
Assumes you keep paying the same amount and finish sooner. Check your lender's overpayment limits and any early repayment charge. An estimate to help you plan, not advice.
- Normal monthly payment
- £1,112
- Paid off in
- 21 yrs 6 mos
- Time saved
- 3 yrs 6 mos
- Interest saved
- £21,142
How overpaying works
Your mortgage charges interest on what you still owe. When you overpay, that extra money comes straight off the balance, so from then on you are charged interest on a smaller amount. The saving compounds: a lower balance means less interest next month, which means more of your normal payment clears the loan, and so on. Even a small regular overpayment can knock years off the term.
To see what your normal payment would be in the first place, use the mortgage repayment calculator.
Common questions
Does overpaying my mortgage save money?
Yes. Every extra pound comes straight off the balance, so you are charged less interest for the rest of the term. Overpay regularly and you clear the mortgage sooner and pay less interest overall, often by thousands of pounds.
Is it better to overpay monthly or with a lump sum?
Both help. A lump sum cuts the balance straight away, so it saves the most interest per pound. Regular monthly overpayments are easier to budget for and add up over time. The calculator lets you try either or both.
Are there limits or penalties on overpaying?
Many lenders let you overpay up to 10% of the balance each year without charge, but fixed-rate deals can have early repayment charges above that. Check your mortgage terms before making large overpayments.
Should I overpay the mortgage or save instead?
Compare your mortgage rate with the interest a savings account would pay. If your mortgage costs more than you could earn in savings, overpaying usually wins. Keep an emergency fund first, and clear pricier debts like credit cards before overpaying a mortgage.
Will overpaying lower my monthly payment or my term?
It depends what you ask your lender to do. By default most reduce the term, which saves the most interest. Some let you keep the term and lower the monthly payment instead. This calculator assumes you keep paying the same amount and finish sooner.
About this calculator
Uses the standard amortisation formula, holding your rate and payment steady and applying overpayments straight to the balance. Real mortgages can have overpayment limits and early repayment charges, and rates change at the end of a deal, so treat the figures as a guide. An estimate to help you plan, not financial advice. Last updated June 2026.