See how much interest you'd save and how much sooner you'd be mortgage-free by overpaying.
Side by side
| Without overpaying | With overpaying |
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Assumes interest is charged monthly on the outstanding balance, your interest rate stays fixed for the whole remaining term, and overpayments reduce the term rather than the monthly payment.
About this calculator
Your normal monthly payment is worked out with the standard repayment mortgage formula from your balance, interest rate and remaining term. The calculator then runs your mortgage forward month by month twice — once paying just that amount, and once paying that amount plus your overpayment (after deducting any lump sum up front) — and compares the total interest and the number of months each takes to clear.
Overpayments are powerful because every extra pound goes straight at the balance rather than at interest, so it immediately reduces the interest charged in every month that follows. That's why overpaying early in a mortgage saves far more than the same overpayment made near the end, and why a lump sum today beats the same amount spread out over years.
This assumes overpayments shorten your term while your monthly payment stays the same — the option that saves the most interest. Some lenders instead reduce your monthly payment and keep the term unchanged, which saves much less, so check which your lender does and ask for the term reduction if you want these numbers.
Worth checking before you commit: many fixed-rate deals cap annual overpayments (often at 10% of the balance) and charge an early repayment fee above that. This is a planning estimate assuming a fixed rate throughout, not financial advice — your actual rate will likely change when you remortgage.
Frequently asked questions
Is it better to overpay monthly or with a lump sum?
Whichever puts money against the balance sooner saves more. A lump sum today beats the same total spread over years, because every month that money is off the balance is a month it is not being charged interest.
Should overpayments reduce my term or my monthly payment?
Reducing the term saves far more interest, because your payment stays the same and the extra keeps attacking the balance. Many lenders default to lowering the payment instead, so ask explicitly for the term reduction.
Is there a limit on how much I can overpay?
Often yes. Many fixed-rate deals cap overpayments at around 10% of the balance a year and charge an early repayment fee above that, so check your mortgage terms before making a large payment.