Mortgage planning
Mortgage overpayment calculator
See how monthly or one-off overpayments could change the interest you pay, your remaining balance and when you could be mortgage-free.
This is not financial advice. The figures are illustrative estimates. Actual results may differ. Read the disclaimer.
Enable JavaScript to explore the calculator. The methodology and frequently asked questions are available below.
How the projection works
Each month, the model adds interest to the outstanding balance, then subtracts the payment. Paying down the balance sooner can reduce the interest charged in later months.
What happens if I overpay by £200 a month? On a £200,000 repayment mortgage with 25 years remaining at a constant 5%, a £200 monthly overpayment could save £41,842.60 in interest and pay off the mortgage 6 years 2 months sooner.
- Repayment mortgage with a fixed annual rate for the whole projection. Interest is added monthly at the annual rate divided by 12.
- The one-off payment is applied today, before any interest. Regular and monthly overpayments start the following month.
- The scheduled monthly repayment stays the same after overpayments. The final payment is capped at the amount owed.
- The model excludes fees, early repayment charges, lender overpayment limits, rate changes and remortgaging.
Results are illustrative. A lender may use daily interest, different payment dates and product-specific rules. Check your mortgage terms before changing payments.
Common questions
How much interest could overpaying save?
It depends on your balance, rate, term and the size and timing of the overpayment. The tool shows the difference between the total interest in the two projections.
Does overpaying change my monthly repayment?
The projection keeps the scheduled payment fixed so overpayments shorten the term or reduce the final instalment. Your lender may recalculate the regular payment, depending on your mortgage terms.
Can my lender charge for overpayments?
Some mortgage products limit how much you can overpay or apply early repayment charges. Check your agreement or ask your lender how it treats extra payments. This tool excludes these charges.
Why might the result differ from my lender’s?
Payment dates, daily interest, rounding, fees and future rate changes can all affect the result. This tool uses monthly interest and shows projected payoff months.