Mortgage cost calculator for the UK and US

Work out what a UK or US mortgage really costs: the monthly payment, the total interest, where your first payment goes, what overpaying saves and what a new rate does when a fix ends.

Your mortgage
Monthly payment
£1,461.48
a month to repay £250,000 over 25 years at 5%
Total interest
£188,443
what the loan costs, if the rate never changes
Total paid back
£438,443
the loan and the interest
Month one
£1,041.67
of the first payment is interest; £419.81 comes off the loan
The loan part overtakes interest
Year 12
after 11 years 2 months of payments, more of each one goes on the loan than on interest

Paying £200 a month extra saves £44,432 in interest and clears the loan 5 years 2 months early, after 19 years 10 months instead of 25 years.

A rate change, side by side

5% throughout
£1,461.48 a month
£188,443 interest
6.58% from year 6
£1,661.52 a month from year 6
£236,454 interest
+£200.04 a month, +£48,011 over the term

If the rate moves to 6.58% at the start of year 6, the payment is £1,661.52, £200.04 a month more, and the loan costs £48,011 more in interest.

This uses monthly interest at the yearly rate divided by 12. UK lenders often work out interest daily, which usually moves the monthly payment by less than a pound. Overpayments keep the payment the same and shorten the term. A rate change re-works the payment over the rest of the term, without overpayments. It leaves out fees, and is general, not about your situation.

Use this calculator to compare a change in interest rate and the lifetime cost of a UK or US repayment mortgage. For an interest-only loan or a one-off lump sum, use the mortgage repayment calculator.

What goes in

Choose the UK, in pounds, or the US, in dollars. Put in the loan, the interest rate and the term, and a monthly overpayment if you’d make one. For the side-by-side part, put in a new rate and the year it starts: year 6 is a five-year fix ending, and year 1 compares two rates for the whole term.

What the result means

The UK example is £250,000 at 5% over 25 years. That’s £1,461.48 a month and £188,443 in interest. In month one, £1,041.67 of the payment is interest, and the part that pays off the loan doesn’t overtake the interest until year 12. Paying £200 a month extra clears it 5 years 2 months early and saves £44,432.

If the fix ends after five years and the rate goes to 6.58%, the Bank of England’s typical revert rate for September 2026, the payment rises to £1,661.52, £200.04 a month more.

The US example is $400,000 at 7.40% over 30 years, Freddie Mac’s average on 15 October 2026. That’s $2,769.52 a month and $597,027 in interest.

How it’s worked out

It uses monthly interest, the yearly rate divided by 12, charged on what you still owe. The payment is the level amount that clears the loan over the term. Overpayments keep the payment the same and shorten the term. A rate change works the payment out again to clear what’s left over the rest of the term, which is what happens when a UK fix ends and you move to the lender’s revert rate. The side-by-side figures leave out overpayments, and nothing here includes fees, PMI, tax or insurance.

Many UK lenders work interest out daily, which usually moves the monthly payment by less than a pound and the total interest by up to a few hundred pounds. In the UK, many lenders let you overpay up to 10% a year without a charge, and the calculator warns you when your overpayments in one of the first five years go over 10% of what you’d owe at the start of that year. In the US, some lenders charge a prepayment penalty.

It’s general, not about your situation.

Sources

Mortgage cost calculator Total mortgage interest Mortgage interest calculator Mortgage overpayment calculator Remortgage calculator Standard variable rate Fix ending 30-year mortgage calculator US mortgage calculator Mortgage calculator UK and US

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