Free UK planning tool · Mortgage
Mortgage repayment & what-if calculator
Calculate monthly payments and total interest, then test what happens with a lump sum, regular overpayments or a higher interest rate. No sign-up, enquiry or credit application is needed to use the calculator.
How the calculator works and what it excludes ↓Market context · Bank of England
Enter the rate you want to test
The quoted-rate feed is unavailable right now. Your own entered rate remains the core assumption in the calculation.
Overpayment scenario
What if you pay a lump sum or more each month?
Model an immediate lump sum and/or a higher regular monthly payment while keeping the original calculated mortgage payment as the baseline. Real products can cap overpayments or charge early-repayment fees, so check the mortgage terms before acting.
Enter either the extra amount or the full monthly payment — the other updates automatically. Your normal modelled payment is £1,267 per month.
Rate sensitivity
What if your mortgage rate is higher?
The full-term totals assume one rate remained unchanged, which is unlikely for many mortgages. The useful point is to see how sensitive the monthly commitment is to a different rate assumption.
Compare this with the monthly amount your household would actually be comfortable carrying.
Save the scenario
Keep the useful numbers in My Money Plan.
Your saved mortgage scenario keeps the payment, rate, term, total interest, stress result and any overpayment assumptions on this device.
Understand the numbers
Mortgage what-if calculator: understand each scenario
Enter the amount you expect to borrow, an annual interest rate and the term in years. For an existing mortgage, use the current balance and remaining term from your lender. Then change one assumption at a time so you can see what is driving the result. The figures are illustrations, not a quote or an application.
What can I test with the mortgage what-if calculator?
Use the same mortgage balance to compare a lump-sum payment, an extra monthly payment or a higher interest rate. For repayment mortgages, the tool models how the payoff time and interest change when you keep the original scheduled payment and add the overpayment. It does not model product switches or lender-specific charges.
How are monthly repayments calculated?
For a capital-and-interest mortgage, the calculation spreads repayment across the selected term using the annual rate divided by 12. The rate is assumed to stay unchanged. At 0% interest, the balance is simply divided by the number of months. Actual lender figures can differ because of daily interest, payment dates, fees and rate changes.
What if I make a lump sum or monthly mortgage overpayment?
For a capital-and-interest mortgage, the lump sum is deducted immediately, then the original calculated monthly payment continues, plus any extra amount entered. This models a shorter term, not a lender reducing your required monthly payment. Interest savings exclude any charges and depend on the assumptions staying the same.
Does this calculate mortgage early-repayment charges?
No. It is an overpayment illustration, not an early-repayment-charge calculator. Check your mortgage offer or ask your lender about the remaining penalty-free allowance, how it is measured and any charges before paying extra. A modelled interest saving is not the net benefit after charges.
What if my mortgage rate is higher?
Enter a higher stress-test rate to compare the modelled monthly payment with the rate you entered first. This is useful for sensitivity planning, but it is not a prediction of your next mortgage rate and it does not reproduce a lender's affordability or stress test.
What does the interest-only result mean?
It estimates monthly interest without paying down the original balance. The capital is still due at the end, and you need a separate way to repay it. The overpayment illustration on this page applies only to capital-and-interest borrowing.
Does the result tell me what I can afford?
No. A repayment figure does not assess income, credit, property or lender criteria. Use the household affordability and budget planner to compare the payment with your own spending. That tool is also a planning estimate, not a lender decision.
Can I save a scenario without an enquiry?
Yes. Save a scenario to keep its payment, term, rate and overpayment assumptions in My Money Plan on this device. This does not submit a mortgage application or contact a professional. Local data may be lost if browser storage is cleared; see the privacy information for details.
Further reading: MoneyHelper — paying off your mortgage early ↗. General information, not a recommendation to overpay.