Mortgage Calculator
Estimate monthly mortgage repayments, total cost and lifetime interest in any major currency.
Your monthly mortgage payment
Pop in your loan details and we'll work out the monthly payment.
How it works
What this calculator does. It estimates the monthly repayment on a mortgage, plus the total amount you'll repay and how much of that is interest. You can use it for a new mortgage, a remortgage, or just to see how a different rate or term would change your monthly cost.
How the calculation works. We take the loan amount, annual interest rate and term in years and apply the standard repayment formula used by lenders. The annual rate is split into twelve monthly periods, and each monthly payment covers both interest on the remaining balance and a slice of the balance itself. Early in the term most of your payment goes on interest; later, more of it chips away at what you owe. If you choose interest-only, your monthly figure only covers the interest — the original balance still has to be repaid at the end.
A worked example. On a £250,000 repayment mortgage at 5% over 25 years, the estimated monthly payment is around £1,461. Over the full term you'd repay roughly £438,000 — meaning about £188,000 of that is interest. Shortening the term to 20 years pushes the monthly payment up to around £1,650, but cuts total interest by tens of thousands of pounds.
How to read the results. "Monthly payment" is what leaves your account each month. "Total repaid" is everything you'll pay across the term, and "Total interest" is the cost of borrowing. Try changing the rate by 1% or the term by 5 years to see how sensitive your payment is — it's a quick way to stress-test affordability.
Figures are estimates only. Your actual offer depends on the lender, product fees, your deposit and your circumstances.
Frequently asked
Complete Guide
How Mortgage Repayments Are Calculated
If you've ever looked at a mortgage offer and wondered how the lender arrived at that exact monthly figure, you're not alone. The maths behind a repayment mortgage isn't magic — it's a single, well-established formula that balances how much you borrow, your interest rate, and how long you take to pay it back.
The three numbers that decide your payment
Every repayment mortgage comes down to three inputs: the amount borrowed (the principal), the annual interest rate, and the term in years. Change any one of these and the monthly payment moves.
A larger loan means a bigger payment. A higher rate means more interest each month. A longer term spreads the payments out, which lowers each one — but increases the total interest you'll pay over the life of the mortgage.
The amortisation formula
Lenders use the standard amortisation formula: M = P · r / (1 − (1 + r)^−n), where P is the principal, r is the monthly interest rate (annual rate ÷ 12), and n is the number of monthly payments (years × 12).
You don't need to crunch the maths by hand. Pop your figures into our mortgage calculator and you'll see the exact monthly figure, plus the total interest you'll pay across the term.
Why early payments are mostly interest
At the start of the mortgage your balance is at its largest, so the interest portion of each payment is at its largest too. As the balance shrinks, the interest shrinks with it, and more of each payment chips away at the principal.
This is called amortisation. By the final years of a 25- or 30-year mortgage, almost all of your payment goes towards paying down the balance.
Fixed vs variable rates
With a fixed-rate deal the rate (and therefore your monthly payment) stays the same for the fixed period — usually 2, 5 or 10 years. With a variable or tracker rate it can move up or down with the Bank of England base rate or your lender's standard variable rate.
After your fixed period ends you'll typically roll onto a higher standard variable rate unless you remortgage. It's worth setting a calendar reminder a few months before the fix ends.