Mortgage Overpayment Calculator
Enter your current mortgage details and a monthly overpayment amount to see how much interest you could save and how many years you could knock off your term.
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Get free mortgage advice from L&C MortgagesHow the mortgage overpayment calculator works
When you make a monthly overpayment on your mortgage, that extra amount reduces your outstanding balance directly. Because interest is charged on the remaining balance each month, a lower balance means less interest accrues — and that saving compounds over time. The calculator simulates your mortgage month by month: each period it calculates the interest on the current balance, applies your standard repayment plus the overpayment, and reduces the balance accordingly. It runs two simulations — one with overpayments and one without — and reports the difference in total interest paid and the number of months saved.
The figures assume your interest rate stays constant for the remaining term. In practice, rates change when you remortgage, so treat the results as an illustration of the overpayment benefit rather than a precise forecast.
Does overpaying make financial sense?
Whether overpaying is the right choice depends on your mortgage interest rate compared to the returns available from savings or investments. If your mortgage rate is higher than the after-tax return you could earn elsewhere, overpaying is likely the more efficient use of spare cash. Also check your mortgage terms — most lenders allow overpayments of up to 10% of the outstanding balance per year without an early repayment charge.
Frequently asked questions
Is there a limit on how much I can overpay?
Most fixed-rate mortgages allow overpayments of up to 10% of the outstanding balance per year without incurring an early repayment charge (ERC). Tracker and variable-rate mortgages often have no limit. Check your mortgage offer document or contact your lender to confirm the rules for your specific product.
Will overpaying reduce my monthly payment or shorten my term?
It depends on how your lender applies overpayments. Some lenders automatically reduce your monthly payment when you overpay; others keep the payment the same and shorten the term instead. Most allow you to choose. Keeping the payment the same and shortening the term saves the most interest overall.
Can I get my overpayments back if I need the money?
Generally no — once paid, overpayments reduce your balance and cannot be withdrawn unless your mortgage has a flexible or offset feature. If you think you might need access to the funds, maintaining a savings account alongside your mortgage may be more appropriate.
How accurate is this calculator?
The calculator assumes a constant interest rate for the full remaining term and uses standard mortgage amortisation mathematics. It is for illustration only. Actual savings will vary if your rate changes at remortgage, if you miss a payment, or if your lender applies overpayments differently.