UK Mortgage Overpayment Calculator
Most UK mortgages let you overpay up to 10% of the outstanding balance each year without penalty. See exactly what an extra £100 or £250 a month does to your interest bill and payoff date.
How to use this calculator
- Enter mortgage balance.
- Enter interest rate.
- Enter remaining term.
- Enter extra monthly overpayment.
- Your results appear instantly below and update as you change the numbers.
How this calculator works
The calculator runs your current amortisation schedule and compares it with the same schedule plus your monthly overpayment. Every overpaid pound goes straight to principal, so it stops accruing interest for the rest of the term — that's why a small overpayment saves disproportionately. The results show your new payoff date, years saved, and total interest saved. Worked example: £200,000 at 4.5% over 20 years costs £103,672 of interest; overpaying £100 a month clears the mortgage in 17 years 9 months and cuts interest to £90,723 — saving £12,949 and 2 years 3 months. Stay inside the 10% annual overpayment limit and you avoid early repayment charges (ERCs).
Frequently asked questions
How much can I overpay without penalty?
Most standard UK mortgages allow overpayments up to 10% of the outstanding balance per calendar year. Above that, early repayment charges typically apply — often 1–5% of the overpaid amount, highest in the first years of a fixed deal. Check your mortgage terms or ask your lender.
Is overpaying the mortgage better than saving or investing?
Overpaying earns a guaranteed, tax-free return equal to your mortgage rate (4.5% in the example above). That beats most cash savings rates in 2026. It can lose to long-term stock market returns, but many people overpay for the certainty — and the 10% allowance resets every year, so you can always pause.
Should I overpay or build a savings buffer first?
Most advisers suggest keeping an emergency fund of 3–6 months of expenses before overpaying — overpaid money is hard to get back. After that, overpaying is usually the best risk-free 'investment' available to a homeowner.
Disclaimer: Results are estimates for general information only and do not constitute financial, tax, or legal advice. Figures reflect the current tax year and may change. Always confirm current limits and consult a qualified professional before making decisions. Official figures: GOV.UK income tax rates · National Insurance · Stamp Duty Land Tax.