Stamp Duty CalculatorMortgage Overpayment Calculator
See how much interest a regular monthly or one-off lump-sum overpayment saves, and how many years it takes off your term. Flags the standard UK 10%-per-year ERC-free allowance that most fixed-rate products allow.
Your mortgage
Overpayment plan
| Metric | Baseline | With overpayment |
|---|---|---|
| Monthly payment | — | — |
| Total paid over term | — | — |
| Total interest paid | — | — |
| Term in months | — | — |
How overpayments work
Every pound of overpayment reduces the principal immediately, so every subsequent monthly interest charge is calculated on a smaller balance. The effect compounds over the remaining term. On a £180,000 balance at 4.85% over 22 years, an extra £200/month typically takes 5-6 years off the term and saves £28,000-£34,000 of interest.
The 10% rule — don't trigger an early repayment charge
Most UK fixed-rate mortgages let you overpay up to 10% of the outstanding balance per calendar year without triggering an early repayment charge (ERC). Above that, the ERC — typically 1-5% of the overpaid amount — can wipe out the interest saving. Check your mortgage offer document for your exact ERC-free allowance. See the ERC calculator for the breach cost, and the breakdown of what remortgaging actually costs if you're weighing an overpayment against switching lender entirely.
Keep the same payment or lower it?
Two ways to apply the saving: shorten the term (keep the payment, finish earlier) or reduce the payment (same term, lower monthly). This calculator assumes you keep the payment and shorten the term — the stronger of the two for total interest saved. If you reduce the payment instead, total interest saved is roughly 40-55% of the figure shown.
Frequently asked questions
How much can I overpay without penalty?
Most UK fixed-rate mortgages allow 10% of the outstanding balance each calendar year ERC-free. Tracker and variable products often allow unlimited overpayment. Check your offer.
Does overpaying hurt my credit?
No. Overpayment is a positive signal. The only downside is cash tied up in the home rather than available as savings.
Is overpaying better than saving?
Mathematically yes, if the mortgage rate exceeds the net-of-tax rate on your savings. In 2026 with mortgage rates around 4.5-5.5% and savings rates around 3-4.5% net, overpaying usually wins. Keep an emergency fund first.
Can I overpay a tracker or SVR mortgage?
Usually with no ERC and no annual cap. Tracker and SVR products are typically fully flexible.
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Last reviewed: 1 October 2026.