UK mortgage calculators
Mortgage Overpayment Calculator
Enter your figures
Your estimate will appear here.
What this result means
An overpayment reduces the balance on which future interest is charged. The useful comparison is not just the first month's interest saving, but the effect on total interest and the illustrated finish date.
How to use the calculator well
- Enter the balance shown on your latest mortgage statement, not the property's value.
- Use the interest rate applying now and the remaining term, rather than the original term.
- Enter an overpayment you could sustain after retaining an emergency buffer.
Worked scenario
On the pre-filled £200,000 balance at 5% over 25 years, compare the normal repayment with an additional £200 each month. The result illustrates the possible interest saving and earlier finish date; it does not predict a lender's daily-interest calculation.
Questions people ask
Can I overpay without a charge?
Only your mortgage terms can answer this. Fixed and discounted deals commonly limit penalty-free overpayments, and an early repayment charge can outweigh the modelled saving.
Should I shorten the term or reduce the payment?
Lenders may apply overpayments differently. Ask how your lender treats them and whether a formal term change requires an affordability assessment.
Sources and review standard
Calculations are independently implemented illustrations and were reviewed on 4 September 2026. We check factual boundaries against MoneyHelper's mortgage cost guidance, FCA consumer mortgage information and relevant lender documentation. Rates and product terms are never presented as live offers.
Before relying on this estimate
This is an educational illustration, not mortgage, financial, tax or legal advice, a lender decision or an offer. Exact rates, fees, early-repayment charges and product rules can materially change the result.
Check the figures with your lender, broker or qualified adviser. Your home may be repossessed if you do not keep up repayments on your mortgage.
Editorial responsibility
Published by Acerville Sparks Limited. Software assists research, drafting and automated formula testing. Primary sources, assumptions and limitations are shown so readers can inspect the work. No independent mortgage professional or financial adviser review is claimed. Reviewed 4 September 2026.