Mortgage overpayment calculator
Overpaying your mortgage clears the balance faster, so you pay interest on a smaller amount for less time. On a £200,000 balance at 4.5% over 25 years, an extra £150 a month saves roughly £29,000 in interest and clears the mortgage almost 5 years early. This free calculator shows your own interest saved and years cut off. It runs in your browser, needs no email, and stores nothing. Check your overpayment allowance first to avoid an early repayment charge.
See what overpaying saves you
Free. No email needed. Runs in your browser, stores nothing.
Interest saved
£29,284
Time cut off the term
4 years and 11 months
Worked example: on a £200,000 balance at 4.5% over 25 years, the normal payment is about £1,112 a month. Adding £150 to make it £1,262 clears the mortgage in about 20 years and 1 month instead of 25 years, saving roughly £29,284 in interest. Change the figures above for your own mortgage.
Simplified illustration for a repayment mortgage at a rate assumed fixed for the whole term. It ignores fees and future rate changes, and assumes your lender allows the overpayment with no early repayment charge. Not a quote and not advice. A regulated broker or your lender can confirm your real figures.
Why a small overpayment does so much
On a repayment mortgage, most of your early payments are interest, not capital. An overpayment goes straight onto the capital, so it removes future interest that would otherwise have built on that money for years. The longer the remaining term and the higher the rate, the more each pound of overpayment is worth. That is why overpaying early in a mortgage saves far more than the same overpayment near the end. See the repayment calculator to see how the balance falls over time.
Check these before you overpay
- Your overpayment allowance. Many deals allow up to around 10% of the balance a year penalty-free. Beyond it you may trigger an early repayment charge.
- Your safety net. Keep accessible emergency savings first, because money overpaid is hard to get back.
- Costlier debts. Clearing high-interest credit cards or loans usually beats overpaying the mortgage.
- Overpay or save. Weigh your mortgage rate against your savings rate: see should I overpay or save.
Common questions
How does overpaying a mortgage save money?
Overpaying reduces the outstanding balance faster, so you are charged interest on a smaller amount for the rest of the term. Because interest builds on the balance every month, taking money off early stops years of interest before it ever accrues. The effect is largest when your rate is high and your term is long.
Is it better to overpay each month or pay a lump sum?
Both help. A regular monthly overpayment is the simplest habit and compounds steadily. A single lump sum saves the most when it is paid early, because the money comes off the balance sooner. This tool models a monthly overpayment; a broker or your lender can model a lump sum against your exact balance.
Will I be charged for overpaying?
Many deals let you overpay up to a set amount each year without penalty, often around 10% of the balance. Overpay beyond that during a fixed or discounted period and you may trigger an early repayment charge. Check your mortgage offer or ask your lender before you start, and see our early repayment charges guide.
Should I overpay or keep the money in savings?
As a rough guide, overpaying wins when your mortgage rate is higher than the after-tax interest your savings would earn. But keep an emergency fund first, since money overpaid is hard to get back, and clear costlier debts before either. Our overpay or save answer walks through the trade-off.
Coming up to a deal ending? See remortgage, or work out a payment change with the payment-shock calculator.
Founder, MortgageExplained, MortgageExplained
Adam spent nearly a decade as a mortgage adviser at Just Mortgages, with further experience in commercial finance. He is CeMAP and CF qualified. He built MortgageExplained to do one thing well: explain mortgages in plain English, then introduce you to a regulated broker when you are ready. Every page is written and reviewed by Adam.
Last reviewed: 21 July 2026