Calculator
Overpayment savings calculator
Every extra pound paid early saves you interest for the rest of the term. For a typical first-time buyer paying £200/month on top, knocking five or more years off the mortgage is realistic. This calculator shows both effects at once.
Your overpayment plan
What you'd save
- Baseline monthly payment
- £1,347
- Payment + overpayment
- £1,547
- Baseline total interest
- £234,917
- With overpayments, total interest
- £168,565
Assumes the overpayment reduces the capital balance immediately and the monthly payment is held constant (so the term shortens). Some lenders apply overpayments only at year-end, some recalculate the monthly payment instead — check your lender's rules. Not financial advice.
The 10% rule on fixed mortgages
Most UK fixed-rate mortgages allow you to overpay up to 10% of the outstanding balance per calendar year without penalty. Exceed it and you usually trigger an Early Repayment Charge (ERC) — often 1-5% of the overpayment amount, depending on the lender and how much fix remains.
Tracker and some offset mortgages allow unlimited overpayments — worth knowing if you have irregular lump sums (bonuses, inheritance) to apply.
When NOT to overpay
- If you have debt at a higher rate (credit cards, personal loans, BNPL arrears), clear those first — they're costing you more than you'd save.
- If you don't have an emergency fund of 3-6 months' essential outgoings. Liquidity matters.
- If your workplace pension match isn't maxed out. Free employer contributions almost always beat mortgage-overpayment arithmetic.