Mortgage overpayment calculator
See how a one-off or recurring overpayment could reduce your mortgage term and interest.
Enter your details
See how a one-off or recurring overpayment could reduce your mortgage term and interest.
When you overpay your mortgage, the extra money goes directly toward reducing your outstanding balance. Because interest is calculated on the remaining balance, a lower balance means less interest each month. This creates a compounding effect — every overpayment saves you more than its face value over the life of the loan.
You can overpay as a one-off lump sum (for example, from a bonus or inheritance) or as a regular monthly or annual extra payment. Both approaches work, and you can combine them. The earlier you overpay, the greater the long-term impact, because the interest savings compound over more years.
Most fixed-rate mortgage deals include an early repayment charge (ERC) if you overpay more than a certain amount — typically 10% of the outstanding balance per year. If you exceed this limit during your fixed period, you may be charged 1–5% of the overpayment amount.
Check your mortgage terms before making large overpayments. Once your fixed deal ends and you move to the lender’s standard variable rate, ERCs usually no longer apply and you can overpay without limit.
When you have spare cash, overpaying your mortgage is one option among several — you could also save, invest, or pay down other debts. Which works out better depends on your interest rates, tax situation, risk tolerance, and personal circumstances.
This calculator shows the interest savings from overpaying your mortgage on your inputs. Some people choose to speak to a qualified financial adviser before making large overpayments, to weigh it against their wider financial picture.
When you overpay, most lenders reduce your term but keep your monthly payment the same. This means you pay off your mortgage sooner and save the most interest overall. Some lenders let you choose to reduce your monthly payment instead, which frees up cash flow but saves less interest in total.
This calculator models the term-reduction approach, which is the most common and usually saves the most interest overall. If flexibility matters more to you than total interest saved, ask your lender about payment reduction.
Interest accrues monthly on the outstanding balance at 1/12th of the annual rate. The regular payment covers interest first, then reduces principal. One-off overpayments are applied at the start of month one; recurring overpayments are applied after the regular payment each month (or each year if annual frequency is chosen). The calculator does not model early repayment charges or lender-specific rules — check your mortgage offer before overpaying. Results are projections based on your inputs.
It depends on your balance, interest rate, and term remaining. This calculator shows the exact interest saving for your inputs — enter your figures and click Calculate to see the projection.
Most lenders apply overpayments to reduce your term while keeping the monthly payment the same. This calculator models that approach. Some lenders let you reduce the monthly payment instead — check your mortgage terms if you prefer that option.
Many fixed-rate mortgages allow overpayments of up to 10% of the outstanding balance per year without charge. Exceeding that limit during the fixed period may trigger an early repayment charge (ERC) of 1–5% of the overpaid amount. Check your mortgage offer document before making large overpayments.
This calculator shows the interest saved on your mortgage with these inputs. Whether putting the same amount into savings or investments would do better depends on the return you assume — that is a personal decision based on your interest rate, tax situation, and risk tolerance. The calculator is a tool for comparing the mortgage side of that calculation.
Need to estimate your base mortgage payment first? Use our mortgage calculator. Buying a new property? The stamp duty calculator estimates your SDLT costs. Considering investing instead of overpaying? The ISA calculator projects how your money could grow tax-free.
Cookies
We use essential cookies to keep the app working. With your permission, we also use analytics cookies to understand what’s working and improve the product. Privacy policy.