Mortgage overpayment questions
What is a mortgage overpayment calculator?
A mortgage overpayment calculator estimates what happens if you pay more than the contractual instalment. It shows the interest you would no longer be charged, and how many months earlier the balance would reach zero.
What the two results mean
Interest saved is the difference between the interest on the original schedule and the interest on the shorter schedule. Months knocked off is the gap between the contractual end date and the month the balance clears if the extra payments continue.
Both figures come from the same idea: each overpayment reduces the balance the lender charges interest on. Later months then accrue less interest, so more of each instalment goes to capital.
What you enter
The useful inputs are the balance still owed, the interest rate, the remaining term, any extra you plan to pay every month, and any one-off lump sum. Changing one of them changes both results. A higher rate, or a longer remaining term, usually makes the same extra payment worth more.
You do not need the original loan amount or the date you bought the house. The remaining balance and the remaining term are what the schedule is built from.
What this calculator assumes
Overpay models a standard repayment mortgage. The contractual monthly payment stays the same, the extra is applied to capital straight away, and interest is charged monthly on the balance. The baseline with no overpayment runs for the term you enter — 25 years is 300 months.
It is an illustration, not a redemption quote. Lenders often charge interest daily, may round differently, and may apply a lump sum on a statement date rather than today. Early repayment charges, fees, and a rate that changes at the end of a fix are outside the sum.
Try the figures in the calculator