Mortgage Overpayment Calculator
Find out how much interest you’d save and how much sooner you’d be mortgage-free by paying extra each month or making a lump-sum overpayment.
Your mortgage
Within the usual 10%-a-year overpayment allowance. Check your own mortgage offer, as some deals differ.
Worked example
A £200,000 mortgage at 4.5% with 25 years left costs £1,111.66 a month and £133,499 in interest over the term.
- Overpay £100 a month: you save about £21,142 in interest and finish 3 years 6 months sooner.
- Overpay £200 a month: you save about £36,280 and finish 6 years 1 month sooner.
- Pay a £10,000 lump sum and keep the same end date: your payment drops to £1,056.08 a month and you save about £6,675.
- Pay the same £10,000 and keep paying £1,111.66: you finish 2 years 2 months sooner and save about £19,300.
Before you overpay
- Know your allowance: usually 10% of the balance a year on fixed and tracker deals. Going over can trigger an early repayment charge.
- Keep an emergency fund: you can’t easily take money back out of your mortgage.
- Clear dearer debts first: a credit card or car finance usually costs far more than a mortgage. Try the loan overpayment calculator.
Need your normal payment first? Use the mortgage calculator.
Sources
Figures are checked against these official sources. Last reviewed 7 November 2026.
Common questions
How much can I overpay my mortgage without a fee?
Most fixed-rate and tracker deals let you overpay up to 10% of the balance each year without an early repayment charge. Some allow more, and standard variable rate mortgages often have no limit. Check your mortgage offer.
Is it better to shorten the term or lower the payment?
Shortening the term saves the most interest, because the balance falls faster. Lowering the payment saves less but gives you more room in your monthly budget. Many lenders lower your payment automatically after a lump sum unless you ask them to keep it the same.
Should I overpay my mortgage or save?
If your savings earn less after tax than your mortgage rate, overpaying usually saves more. But keep an emergency fund first, because money paid into a mortgage is hard to get back, and clear more expensive debts such as credit cards and car finance before overpaying.
Do overpayments reduce my monthly payment?
Regular monthly overpayments usually shorten the term and keep the payment the same. Lump sums often lower the payment. Lenders differ, so ask yours how it applies overpayments.