Mortgage Overpayment Calculator
Estimate onlyOverpaying reduces the balance that interest is charged on, so it can cut both the total interest and the length of your mortgage. This tool illustrates the difference between keeping your current payment and adding an overpayment.
Estimated interest saved
£33,849
And around 5 years off the term.
Current monthly payment
£1,169.18
New monthly payment
£1,319.18
Time saved
5 years
New estimated repayment period
20 years 1 month
Interest without overpaying
£150,754
Interest with overpaying
£116,905
Things to be aware of
- Most UK lenders allow overpayments of up to 10% of the outstanding balance each year without charge, but limits and early repayment charges vary by product. Check your mortgage offer before overpaying.
Estimate only
How this calculation works
We calculate your contractual monthly payment from the balance, rate and remaining term, then run two month-by-month simulations: one with the contractual payment only, and one with your overpayment (plus any lump sum every twelfth month). The difference in months and in total interest is shown.
contractual payment M = P · r ÷ (1 − (1 + r)^−n)
each month: interest = balance × r; balance = balance + interest − (M + overpayment)
saving = interest(no overpayment) − interest(with overpayment)Assumptions
- The interest rate stays the same for the remaining term.
- Overpayments are made every month and reduce the term rather than the payment.
- No early repayment charges or overpayment limits are applied.
Limitations
- Most lenders cap penalty-free overpayments, commonly at 10% of the balance a year.
- Interest calculation frequency varies between lenders.
- Overpaying is not automatically the best use of money; this tool does not advise you.
Last reviewed: 1 September 2026 · Calculation version 1.0.0
Next in your journey
Remortgage Calculator
Compare your current payment with an illustrative new deal, including fees and a break-even period.
Open Remortgage calculator