Mortgage overpayment calculator
See what an extra monthly payment could do to your mortgage.
Page checked: 21 October 2026
Enter your mortgage
What the result means
The model uses standard amortisation. Your lender may apply overpayments differently, particularly on fixed-rate mortgages, so check the mortgage terms before acting.What the overpayment result shows
This calculator uses standard mortgage amortisation to estimate how an extra monthly payment could affect the balance, interest and payoff time. It is most useful for comparing scenarios: for example, no extra payment versus €50, €100 or €250 extra each month.
The result is not a promise that your lender will shorten the mortgage by the same amount. Some lenders reduce the monthly repayment instead, while others may allow you to keep paying the same amount and finish earlier. Fixed-rate mortgages can also have overpayment limits or charges.
Before you make the payment
Check the lender's overpayment rules, whether there is a penalty or annual allowance, and how the payment will be allocated to the capital. If you are deciding between overpaying and retaining cash, read overpay or save? and should I overpay?.
Should I overpay my mortgage?
Read the practical checklist before making extra payments.
Read the guide →How to compare overpayment scenarios
For a useful comparison, run the same mortgage details three times: with no extra payment, with a manageable monthly overpayment, and with a one-off lump sum. Keep the balance, rate and remaining term the same in each scenario so that the differences are easier to interpret.
| Scenario | What to look at |
|---|---|
| No overpayment | Use this as the baseline for remaining interest and expected payoff date. |
| Monthly extra payment | Check the estimated interest reduction and whether the extra payment is sustainable every month. |
| One-off lump sum | Compare the interest saving with the value of keeping an emergency fund available. |
These calculations assume the extra money reduces the mortgage balance as modelled. Your lender may instead reduce the scheduled repayment, restrict overpayments on a fixed rate, or apply charges. Ask how your payment will be treated before sending it. For the wider decision, read overpay versus save and paying off a mortgage early.
Sources & important note
Information is for general information only. Mortgage rules, rates, lender criteria and costs can change. Always confirm the current position with the relevant lender or official source before making a financial decision.