Free first-time buyer calculator
Mortgage Overpayment Calculator
Explore how paying a little extra each month could change how long a mortgage lasts and what it costs.
Add your numbers
Explore an overpayment scenario
See how paying a little extra each month could change how long a mortgage lasts and the interest it costs.
Many lenders cap fee-free overpayments (often around 10% of the balance each year) and some charge early repayment fees. Check your mortgage terms first.
Read MoneyHelper on paying a mortgage off early ->Live estimate
Updates as you typeWhat the extra could change
Interest saved
£37,975
Compared with paying the standard amount for the whole term.
Mortgage-free in
25y 4m
Time saved
4y 8m
Standard payment
£1,208/mo
With overpayment
£1,308/mo
Estimate only. This is not a mortgage offer, affordability assessment, eligibility decision or recommendation.
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How this mortgage overpayment calculator works
A mortgage overpayment is any amount you pay on top of your normal monthly payment. Because the extra money reduces the balance straight away, less interest builds up each month afterwards — which is why even small regular overpayments can shorten a mortgage by years.
This calculator simulates a UK repayment mortgage month by month. It works out the standard monthly payment from your mortgage amount, interest rate and term, then adds your chosen overpayment and tracks the balance until the mortgage is repaid. The result shows how much sooner the mortgage could end and how much interest that could save, compared with paying the standard amount for the whole term.
The figures are illustrative estimates. Real mortgages move between rates and deals, and lenders apply overpayments in different ways, so treat the results as a way to explore the idea rather than a prediction.
Common questions
How much can you overpay on a mortgage without a fee?
Many UK lenders let you overpay up to around 10% of the outstanding balance each year without an early repayment charge, but allowances vary between lenders and deals. Your mortgage offer or annual statement sets out your exact allowance, and your lender can confirm it.
Does overpaying a mortgage reduce the term or the monthly payment?
Lenders usually offer a choice: keep the same monthly payment and finish sooner, or keep the same end date and pay less each month. This calculator illustrates the first option — a shorter term with less interest overall. Ask your lender how they apply overpayments by default.
Is it worth overpaying a mortgage?
It depends on your interest rate, any early repayment charges, whether you have more expensive debt, and whether you would be left without an emergency fund. This tool only shows the mortgage side of the sums. MoneyHelper's guidance on paying off a mortgage early covers the trade-offs, and a regulated adviser can talk through your circumstances.
Do overpayments work on interest-only mortgages?
This calculator models a repayment mortgage, where each payment covers interest and reduces the balance. Overpayments on an interest-only mortgage also reduce the balance, but the sums work differently — check with your lender how they would treat an overpayment.
How is the interest saving calculated?
The tool runs the same month-by-month simulation twice: once with the standard payment only, and once with your overpayment added. The interest saving is the difference in total interest between the two runs, so both figures come from the same method.
Keep learning
Plain-English guides that pair well with this tool: