UK Mortgage Overpayment Calculator
See how much interest you save and how many years you knock off your mortgage
Debt Details
Enter your loan information to see how a fixed overpayment reduces your debt faster
UK Mortgage Overpayment Rules
Most UK residential mortgages allow you to overpay up to 10% of the outstanding balance per year without triggering an Early Repayment Charge (ERC). This means on a £250,000 mortgage you can typically pay an extra £25,000 per year penalty-free. Always check your mortgage terms — tracker and SVR mortgages often have no limit at all.
Overpaying reduces the outstanding balance on which interest is charged, so every pound of overpayment saves you interest for the remaining term. A £200/month overpayment on a £200,000 mortgage at 4.5% could save over £25,000 in interest and shave 5+ years off your term.
Should You Overpay Your Mortgage or Invest?
This is one of the most debated questions in the UK FIRE community. The answer depends on your mortgage rate versus your expected investment return:
- If your mortgage rate is higher than your expected after-tax investment return, overpaying is mathematically better.
- If your mortgage rate is lower than your expected ISA or index fund return, investing may generate more wealth over time.
- Many UK FIRE planners do both — overpay within the ERC limit and invest the rest into a Stocks and Shares ISA.
A paid-off mortgage dramatically reduces your monthly outgoings, which lowers the income your portfolio needs to generate and can bring your FIRE date closer.
Frequently Asked Questions
How much can I overpay my UK mortgage without a penalty?
Most UK fixed-rate mortgages allow up to 10% of the outstanding balance per year without an Early Repayment Charge. Check your mortgage offer document or call your lender to confirm your specific allowance.
Is it better to overpay my mortgage or invest in an ISA?
If your mortgage rate is higher than your expected investment return, overpaying wins mathematically. If lower, a Stocks and Shares ISA may generate more wealth. Many FIRE planners do both.
Do overpayments reduce the term or monthly payment?
Most UK lenders apply overpayments to reduce the remaining term by default, keeping your monthly payment the same. Some allow you to choose. Reducing the term saves more interest; reducing the payment improves monthly cash flow.
What happens to my loan-to-value ratio when I overpay?
Overpayments reduce your outstanding balance, improving your loan-to-value (LTV) ratio. A lower LTV typically unlocks better mortgage rates when you remortgage — an additional benefit beyond just the interest saved.
This calculator is for illustrative purposes only and does not constitute financial advice. Mortgage terms vary by lender. Always check your Early Repayment Charge rules before making overpayments. Consult a mortgage broker or financial adviser for advice specific to your situation.
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