Mortgage
calculator.

01 / START WITH YOUR NUMBERS

How to use the mortgage calculator

1. Start with the property and deposit

   Enter a purchase price and the cash deposit you plan to put towards it. The difference is the mortgage amount. A larger deposit reduces the balance in this calculation; it does not automatically change the interest rate.

2. Choose a rate and term

   Use an annual mortgage interest rate, not APRC. The term is the time over which you repay the borrowing, which can be much longer than the period covered by a fixed-rate deal. Try a higher rate too, to see the effect on the payment.

3. Check the repayment type

   Repayment mode clears the balance through regular payments. Interest-only mode pays interest each month and leaves the original mortgage amount to repay at the end. Compare the final balance as well as the monthly figure.

02 / THE NUMBERS IN PRACTICE

A worked example

This illustration uses a £300,000 property, a £60,000 deposit and a 25-year repayment mortgage at 4.5% annual interest. The £240,000 borrowing is 80% of the property price. The rate is an example, not a quote.

03 / UNDERSTAND YOUR RESULT

What happens when you change the deposit?

At a fixed rate and term, the payment moves in proportion to the mortgage balance. Reducing a £240,000 balance by £24,000 reduces the estimated payment by 10%. The deposit is paid separately, so it is not included in the total mortgage repayments shown.

The loan-to-value figure divides the mortgage by the property price. For a £300,000 property, £240,000 borrowing is 80% LTV and £210,000 borrowing is 70% LTV. These are arithmetic comparisons, not lending thresholds or promises of a particular rate.

04 / UNDERSTAND YOUR RESULT

A mortgage term is not a fixed-rate deal

The calculation holds the interest rate constant for the whole term to make scenarios comparable. If an initial deal ends after a few years, the rate and payment can change. A whole-term interest estimate should therefore be read as an illustration, not a forecast of the actual interest you will pay.

A lower monthly figure can come from extending the term rather than reducing the cost. Check the total interest and any balance due at the end. MoneyHelper explains repayment and interest-only mortgages in its mortgage guidance below.

PLAIN ENGLISH, PLEASE

Mortgage glossary

The terms behind the inputs and results, explained without the guesswork.

Deposit

Cash you put towards the purchase before mortgage borrowing. It is separate from stamp duty and moving costs.

Mortgage balance

The amount financed. Here it is the property price minus the deposit.

LTV

Loan to value: the mortgage balance divided by the property value, expressed as a percentage.

Repayment mortgage

A model where regular payments cover interest and reduce the borrowed amount to zero by the end.

Interest-only

Payments cover interest while the borrowed amount remains outstanding. The final balance must be repaid separately.

APRC

Annual percentage rate of charge, a mortgage cost comparison measure. This calculator instead requires the annual interest rate used for repayments.

BEHIND THE ESTIMATE

How the calculation works

We subtract the deposit from the property price, divide annual interest by 12 and calculate a level monthly payment across years × 12 payments. At zero interest, the repayment is simply the balance divided by the payment count.

Interest-only payments equal the balance multiplied by the monthly rate. The total then includes all interest payments plus the original balance due at the end. No deposit, fees, purchase tax, insurance or rate changes are added. Displayed values are rounded; totals use unrounded payments.