Mortgage overpayment calculator
Mortgage overpayment calculator UK: what difference do extra payments make?
Model a regular monthly overpayment, a one-off lump sum, or both. The calculator compares the default repayment path with a faster one so you can see the trade-off in plain numbers.
Illustrative only. Review assumptions and disclaimer details before relying on the outputs.
Useful for
- Deciding whether a bonus should go to the mortgage.
- Seeing if overpaying saves meaningful time as well as interest.
- Pressure-testing a plan before checking lender overpayment limits.
What this tool is for
- Pressure-test a budget before an agreement in principle.
- Compare simple scenarios without handing data to a lead form.
- Understand how rates, deposits, and monthly costs change the picture.
Quick notes about this tool
Useful for
- Deciding whether a bonus should go to the mortgage.
- Seeing if overpaying saves meaningful time as well as interest.
- Pressure-testing a plan before checking lender overpayment limits.
What this tool is for
- Pressure-test a budget before an agreement in principle.
- Compare simple scenarios without handing data to a lead form.
- Understand how rates, deposits, and monthly costs change the picture.
Your scenario updates the page URL so you can revisit it later.
Current monthly repayment
£1,486
With overpayments
£1,736
Interest saved
£77,143
Time saved
8 years
Repayment comparison
What this means
Overpayments help most when your rate is meaningful and the mortgage still has a long runway left.
- This example trims roughly 8 years and saves £77,143 in interest if you can keep the extra payments up.
- If cash flow is uncertain, a one-off lump sum can be less stressful than committing to a bigger monthly overpayment forever.
- Check your lender's overpayment limit before treating this as the final answer, especially if you are still in a fixed-rate period.
How to use this mortgage overpayment calculator
Enter the remaining mortgage balance, current rate, and remaining term. Then test one regular monthly overpayment, one lump sum, or a combination of both to see how the payoff timeline and total interest change.
If you want the broader decision context first, read is it better to overpay your mortgage? alongside the calculator.
What affects the result most
- The earlier in the mortgage you overpay, the more time interest has to stop compounding.
- Higher rates generally make overpayments look more valuable.
- If your emergency cash would become too thin, the mathematical answer may still be the wrong practical answer.
If your current payment already feels tight, it can help to sense-check affordability again using the mortgage affordability calculator.