Mortgage repayment calculator
Your monthly payment and total interest, for any loan, rate and term.
Standard repayment mortgage, rate held flat for the whole term — real deals reprice every few years. Illustration only, not financial advice.
A repayment mortgage charges interest on whatever you still owe, and each monthly payment covers that month’s interest plus a slice of the loan itself. Early on, most of the payment is interest; by the final years it is almost all capital. The calculator uses the same amortisation formula lenders use, so the monthly figure should match a lender’s illustration for the same loan, rate and term to within pennies.
Two levers move the number. The rate moves it fast: on a £200,000 loan over 25 years, each 1 percentage point costs or saves roughly £110 a month. The term moves it more sneakily: stretching from 25 to 35 years cuts the monthly payment, but you pay interest for a decade longer — often £50,000 or more in extra interest on a typical loan. Cheaper per month is not the same as cheaper.
One honest caveat: almost nobody pays a single rate for the whole term. A typical fix lasts 2 or 5 years, after which you remortgage or roll onto the lender’s (usually much higher) standard variable rate. Treat the total-interest figure as an illustration at today’s rate, not a prediction — and re-run the sums with a pessimistic rate before you commit to a loan size.
Common questions
How much would a £200,000 mortgage cost per month?
At 4.5% over 25 years, about £1,112 a month on repayment terms, and roughly £133,500 of total interest over the term. At 5.5% it rises to about £1,228; over 35 years at 4.5% it falls to about £946 a month but total interest climbs past £197,000. The calculator lets you test your own combination.
How is a mortgage payment calculated?
Lenders use a standard amortisation formula: the monthly rate (annual rate ÷ 12) applied so that equal payments clear both interest and capital exactly by the end of the term. You don’t need the algebra — but it explains why doubling the loan doubles the payment, while doubling the term does not halve it.
Is a longer mortgage term a bad idea?
Not automatically — a 30- or 35-year term can be the difference between affording a home and not, and you can usually overpay or shorten it later. The trap is drifting: taking the long term for breathing room and never revisiting it. Each extra 5 years on a £200,000 loan at 4.5% adds roughly £30,000–£35,000 of interest.
What happens when my fixed rate ends?
You move onto the lender’s standard variable rate — typically 2–3 percentage points higher — unless you remortgage or take a new deal with your current lender. Diarise it for 6 months before the fix ends: you can usually lock a new rate that far ahead, and it is one of the few genuinely free wins in home ownership.
Numbers are half the story. Check the home itself.
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