UK Mortgage Calculator

How to use the mortgage calculator

Enter the price of the property you're looking to buy, the deposit you have available (as either a cash amount or a percentage), the mortgage term in years, and the interest rate you've been quoted or expect to be offered. The calculator instantly works out your loan amount, loan-to-value (LTV), monthly repayment, total interest over the term, and a year-by-year breakdown of how much of each payment goes towards interest versus paying down the capital you borrowed.

This is designed for a standard capital repayment mortgage — the most common type in the UK, where you pay off both the interest and a portion of the loan itself every month, so the balance reaches zero at the end of the term. If you're comparing an interest-only mortgage, remember that your monthly payment will be lower, but none of it reduces the capital you owe — you'll need a separate repayment plan for the full loan amount at the end of the term.

The mortgage repayment formula

UK lenders calculate capital repayment mortgages using a standard annuity formula. In plain terms, your monthly payment (M) is worked out from the loan amount (P), the monthly interest rate (r, your annual rate divided by 12), and the number of monthly payments over the term (n):

M = P × [r × (1 + r)ⁿ] ÷ [(1 + r)ⁿ − 1]

This formula guarantees that if you pay exactly M every month for n months at a constant rate r, your balance will be reduced to precisely zero at the end of the term — with the interest portion shrinking and the capital portion growing every month as your outstanding balance falls.

Worked example

Say you're buying a home for £300,000 with a 15% deposit (£45,000), leaving a mortgage of £255,000. You're offered a 25-year term at a fixed 4.5% interest rate.

Plugging those numbers into the formula above gives a monthly repayment of roughly £1,417. Over 25 years (300 monthly payments) you'd repay a total of around £425,000, of which about £170,000 is interest and £255,000 is the capital you originally borrowed. In year one, the majority of each monthly payment is interest — around £950 of the £1,417 — but by year 20, most of each payment is chipping away at the capital instead.

Try adjusting the deposit or the term in the calculator above: increasing your deposit to 25% (£75,000) on the same property drops the loan to £225,000 and cuts the monthly repayment to around £1,251, saving roughly £166,000 in interest over the life of the loan compared with a smaller deposit and shorter equity buffer.

What affects your mortgage rate

UK mortgage lenders price their rates based mainly on your loan-to-value (LTV) — the size of your mortgage relative to the property's value. A lower LTV (bigger deposit or more equity) typically unlocks cheaper rates because the lender's risk is lower if property prices fall. Your credit history, income, existing debts and the Bank of England base rate all play a part too. Fixed-rate deals are priced using swap rates (the cost of borrowing on financial markets for that fixed period), while tracker and variable rates move directly with the Bank of England base rate.

Things this calculator doesn't include

This tool gives you the core repayment figures so you can compare scenarios quickly, but a full mortgage offer will also include arrangement or product fees (often £0–£1,999, sometimes added to the loan itself), a valuation fee, legal (conveyancing) costs, and potentially an early repayment charge if you switch deals before a fixed or discounted period ends. It also assumes your interest rate stays constant for the whole term — in reality, most UK mortgages have an initial fixed or discounted period (commonly 2–5 years) after which you'll move onto the lender's standard variable rate unless you remortgage.

Related calculations to check next

Buying a home almost always means paying Stamp Duty Land Tax (or LBTT in Scotland, LTT in Wales) on top of your deposit and mortgage — use our stamp duty calculator to work out that cost before you make an offer. It's also worth checking your take-home pay to make sure the monthly repayment comfortably fits your budget alongside your other outgoings.