Mortgage Overpayment Calculator
See exactly how much interest you'd save, and how many years you'd clear your mortgage early, by overpaying. Free, instant, and nothing you enter here is stored or sent anywhere.
This is a one-time snapshot. Bunse tracks it for real.
Log your actual mortgage, product and rate changes, and real overpayments as you make them — and watch this same projection update as your balance actually moves, without opening a spreadsheet or connecting your bank.
Try Bunse free →How mortgage overpayments work
Every mortgage payment splits into two parts: interest on what you still owe, and a bit that actually reduces the balance. Early on, most of your payment is interest — the balance is at its highest, so the interest charged against it is too.
An overpayment goes almost entirely toward the balance itself, since your normal payment already covers that month's interest. A smaller balance means less interest charged next month, which means more of next month's normal payment reduces the balance too — the effect compounds for the rest of the mortgage, which is why even a modest, regular overpayment adds up to more than its face value in savings.
Most UK lenders keep your monthly payment the same when you overpay and simply let you finish early, rather than reducing what you owe each month — that's what this calculator assumes, and it's usually the better outcome if you can afford to keep paying at the current rate.
Common questions
Is it worth overpaying my mortgage?
Usually, if your mortgage rate is higher than what you'd earn after tax on the same money in savings, and you already have an emergency fund in place. Overpaying guarantees a return equal to your mortgage rate, which is hard to beat risk-free elsewhere — but check for early repayment charges first, and make sure you're not leaving yourself without a cash buffer.
How much can I overpay on my mortgage without a penalty?
Most UK lenders let you overpay up to 10% of your outstanding balance each year, penalty-free, while you're in a fixed or tracker deal. Above that, an Early Repayment Charge (ERC) usually applies — typically 1–5% of the amount over the limit. Check your mortgage offer document or ask your lender directly, since terms vary.
Should I overpay my mortgage or pay into a pension?
This depends on your tax position, employer pension matching, and how close you are to retirement — it's a genuine financial planning question, not a simple calculation. If your employer matches pension contributions, that match is usually worth taking first since it's an immediate guaranteed return. Beyond that, speak to a qualified financial adviser about your specific circumstances.
Does overpaying reduce my monthly payment or shorten my term?
Usually the term — most UK lenders keep your monthly payment the same and simply let you finish paying off the mortgage earlier, which is also how this calculator works. Some lenders offer the option to reduce your monthly payment instead; check with yours if that's what you'd prefer.
How accurate is this calculator?
It runs the same month-by-month amortisation Bunse uses in the app itself — a standard repayment calculation, not a rough estimate. It's a projection based on the figures you enter, though, not a substitute for your lender's official redemption statement, and it doesn't account for rate changes over the term, fees, or interest charged on a different compounding basis than monthly.
Is this financial advice?
No. This is a calculation based on figures you enter, not a recommendation. Speak to a qualified financial adviser or mortgage broker for advice specific to your circumstances.
Nothing you enter here goes anywhere
This calculator runs entirely in your browser. There's no form submission, no server, no account — the numbers you type never leave your device. It's the same principle behind the rest of Bunse: no bank connections, nothing stored anywhere but your own device.
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