Mortgage Overpayment Calculator

Overpaying a UK mortgage is one of the simplest ways to cut tens of thousands of pounds in interest and clear your home loan years earlier. This calculator models regular monthly overpayments and one-off lump sums against your current balance, rate and remaining term, then shows the interest saved and the new payoff date — alongside an Early Repayment Charge warning if you exceed the typical 10% annual allowance on a fixed-rate deal. With 2025/26 fixed rates sitting around 4.5-5.5% on 2-year deals and roughly 4.7% on 5-year fixes, every £100/month overpaid on a £200,000 mortgage at 5% saves around £20,000-£25,000 in interest and shortens the term by 4-5 years. The maths is essentially a guaranteed, tax-free return at your mortgage rate — hard to beat for risk-free savers in the basic-rate band. This tool is for homeowners on a repayment mortgage who have spare cash flow after building a 3-6 month emergency fund and maxing out higher-priority pots like workplace pension matching. It is also useful for borrowers approaching the end of a fixed deal who want to chip the balance down before remortgaging to a lower loan-to-value (LTV) band — moving from 75% to 60% LTV can unlock a noticeably better rate. What the calculator does NOT model: Early Repayment Charges on the excess above 10%, offset mortgage mechanics, interest-only loans, buy-to-let where Section 24 affects the trade-off (overpaying reduces interest you could claim as a 20% tax credit), or the option to drawdown overpayments later via flexible mortgages. It assumes your overpayments come straight off the capital and the lender keeps the original term while shortening it informally. Regional notes: the maths is identical across England, Scotland, Wales and Northern Ireland — mortgage regulation is UK-wide via the FCA. For wider context, also check the main Mortgage calculator, the Remortgage break-even tool and our Compound Interest calculator to compare overpaying against investing in a stocks and shares ISA.