Mortgage Interest Calculator
Enter the property price, deposit, interest rate and term to see your monthly mortgage repayment and a built-in interest rate stress test. Free and instant.
Enter the mortgage details
How the mortgage calculator works
Enter the property price and your deposit; the difference is the amount you borrow. The calculator applies your interest rate over the term to work out the monthly repayment on a capital-and-interest (repayment) mortgage, and shows how much interest you pay in total.
For a tracker mortgage the rate is the Bank of England base rate plus your lender's margin. For a fixed rate, enter the fixed figure and leave the margin at zero.
The rate stress test
Because rates can rise, the calculator also shows your repayment if the rate were 1 and 2 percentage points higher. UK lenders apply a similar stress test when they assess affordability, so it's worth checking you could still afford the higher figure before you commit.
Ways to reduce the interest you pay
- A larger deposit means a lower loan-to-value (LTV) and usually a better interest rate.
- A shorter term raises the monthly payment but cuts the total interest sharply.
- Overpayments (many lenders allow up to 10% a year penalty-free) shorten the term and save interest.
- Remortgage before your fixed deal ends to avoid slipping onto the lender's higher standard variable rate.
Frequently asked questions – Mortgage Interest Calculator
Most UK lenders want at least 5–10% of the property price, but a bigger deposit unlocks lower rates. At 25% deposit (75% LTV) you'll typically reach the better rate bands. First-time buyers can boost a deposit with a Lifetime ISA, which adds a 25% government bonus.
A fixed rate stays the same for a set period (typically 2–5 years), so your payment is certain. A tracker follows the Bank of England base rate plus a fixed margin, so it moves up and down with the base rate. Use the base rate + margin fields for a tracker, or the fixed figure for a fix.
A longer term (say 35 years instead of 25) lowers the monthly payment but increases the total interest considerably. If you can afford the higher payment, a shorter term saves a lot over the life of the mortgage. The stress test helps you judge what's comfortable.
It's a close estimate. A lender's illustration will factor in product fees, your exact completion date and any cashback, so treat this as a guide and use the lender's official mortgage illustration for the precise figures.