Mortgage Overpayment Calculator
See how much interest and time you could save by making extra mortgage payments — monthly overpayments, one-off lump sums, or both.
How mortgage overpayments work
A mortgage overpayment is any amount you pay above your required monthly repayment. The extra money goes directly toward reducing your outstanding balance, which means you pay less interest over the life of the mortgage and finish paying it off sooner.
Even small regular overpayments can make a significant difference. Overpaying £200/month on a £250,000 mortgage at 4.5% over 25 years could save you over £30,000 in interest and take more than 5 years off your mortgage term.
Most UK mortgage lenders allow you to overpay up to 10% of your outstanding balance each year without incurring an early repayment charge (ERC). Check your mortgage terms before making large overpayments, especially during a fixed-rate period.
Frequently asked questions
- How are mortgage overpayment savings calculated?
- The calculator runs a month-by-month amortisation schedule twice — once with your standard repayments, and once including your overpayments. The difference in total interest paid is your saving. Lump sums are applied immediately, reducing the balance before interest is calculated.
- Is there a limit on how much I can overpay?
- Most UK lenders allow you to overpay up to 10% of your outstanding mortgage balance per year without an early repayment charge (ERC). Beyond this, you'll typically face a fee of 1–5% of the excess. Check your mortgage terms — some products allow unlimited overpayments.
- Should I overpay my mortgage or save the money?
- It depends on your mortgage rate versus your savings rate. If your mortgage rate is 4.5% and your savings earn 3%, overpaying your mortgage gives a guaranteed better return. However, building an emergency fund first is generally advisable. Overpaying also locks up your money — you can't easily access it again.
- Do early repayment charges apply to overpayments?
- ERCs typically apply during a fixed-rate or discounted period. Most lenders allow penalty-free overpayments up to 10% of the balance per year. Once you're on the lender's standard variable rate (SVR), you can usually overpay without restriction. Always check your specific mortgage terms.
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Estimates only, based on the assumptions you enter and current published rates. Not financial advice. Your actual costs depend on your circumstances and your lender. HomeThink is not authorised or regulated by the Financial Conduct Authority and recommends no lender or mortgage.
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