Mortgage Overpayment Calculator

See how much interest you could save, and how many years you could knock off your mortgage, by overpaying a little each month or paying in a lump sum.

Free tool Updated June 2026 2 min
£
%
yrs
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Interest saved
£0
Time knocked off
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Without overpaying,
With your overpayments,

Enter your balance, rate, years left and an overpayment to see the impact.

How overpaying saves you money

Your mortgage charges interest on the balance you still owe. Overpay, even a modest amount each month, and that balance falls faster, so less interest builds up and you clear the mortgage sooner. Usually your monthly payment stays the same and it's the term that shortens, which is where the big saving comes from.

Should you overpay?

Overpaying tends to be worthwhile when your mortgage rate is higher than what your savings earn after tax, you've cleared any higher-interest debt, and you still have an emergency fund. If you'd be better off topping up a pension (especially with an employer match) or you might need the cash soon, think twice. Our mortgage rates guide helps you see where your rate sits.

Watch out for early repayment charges

Most fixed deals let you overpay up to 10% of the balance a year with no penalty. Go beyond that and you could face an Early Repayment Charge (ERC), often a percentage of the amount. Always check your lender's annual allowance first. If you're near the end of a deal, our remortgage guide covers your options.

Want to talk through whether overpaying or remortgaging is the smarter move for you? Debbie at DS Financial is happy to help, no pressure.

General information, not financial advice. The calculator is an estimate, your lender's exact figures may differ. Check your overpayment allowance before paying.

FAQs

Overpayment FAQs

Should I overpay my mortgage?
It often makes sense if you have spare cash, your savings earn less interest than your mortgage rate, and you've no higher-interest debts or pressing need for the money. Overpaying cuts the interest you pay and can clear the mortgage years early. But keep an emergency fund, and weigh it against pension contributions.
Are there penalties for overpaying?
Many fixed-rate deals let you overpay up to 10% of the balance each year penalty-free. Go over that and you may pay an Early Repayment Charge (ERC). Always check your lender's annual overpayment allowance first.
Does overpaying reduce my term or my monthly payment?
Usually it reduces the term (you finish sooner) while your monthly payment stays the same, that's where the big interest saving comes from. Some lenders let you choose to lower the payment instead; ask which applies.
Is it better to overpay or to save?
Roughly: if your mortgage rate is higher than the interest (after tax) you'd earn on savings, overpaying usually wins. If savings pay more, or you might need the money, saving can be better. Clearing high-interest debt and getting any employer pension match usually come first.
Can I make a one-off lump-sum overpayment?
Yes, most lenders accept lump sums, subject to the same annual allowance and ERC rules. A lump sum early in the term saves the most interest. The calculator above lets you model both regular and one-off overpayments.

Found this useful? If you'd rather talk it through with a real broker, book a free chat with DS Financial, the regulated mortgage adviser.

Book a free chat with DS Financial

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