How does mortgage overpayment work in the UK?
Most UK mortgages allow you to overpay up to 10% of the original loan amount each year without triggering an Early Repayment Charge (ERC). When you overpay, the extra payment goes directly against the principal — the outstanding balance — rather than the interest portion of your monthly payment. Because mortgage interest is calculated each month against the remaining balance, reducing that balance immediately means every future month accrues less interest. Over a 25-year term, even modest monthly overpayments compound into many thousands of pounds saved and several years shaved off the mortgage.
Should I overpay my mortgage or invest the money instead?
The straightforward comparison is interest rate vs expected investment return. If your mortgage rate is 5% and you can earn 7% in a Stocks and Shares ISA after charges, mathematically investing wins on average. But the comparison is rarely that simple. Mortgage overpayments deliver a guaranteed, risk-free return equal to your mortgage rate, while investments carry volatility and can lose value over the short term. There's also the psychological pull of being debt-free sooner. Tax-efficient wrappers like ISAs and pensions can change the maths significantly — pension contributions attract 20–45% tax relief upfront, often beating mortgage rates outright. A balanced approach — overpaying part, investing part — suits most people. This is general guidance, not financial advice; speak to a qualified adviser for your situation.
What are early repayment charges and when do they apply?
Early Repayment Charges typically range from 1% to 5% of the outstanding balance and apply during the fixed-rate or discounted period of your mortgage. Most lenders waive ERCs on overpayments up to 10% of the original loan per year — anything above that incurs the charge on the excess. Once you're on the lender's standard variable rate (after the fixed period ends), ERCs usually no longer apply. Always check the offer document for your specific limit before making a large overpayment. If you're still in the buying process, our UK stamp duty calculator shows the SDLT due on completion. If you're a contractor planning a mortgage, also see our IR35 inside vs outside calculator to understand your true take-home.