About this calculator
This mortgage calculator shows the monthly repayment for a capital-and-interest mortgage, your loan to value (LTV), the total you'll repay and how much a rate change would move your payment.
To see how much you might be able to borrow, use the mortgage affordability calculator instead.
How the calculation works
Mortgage = property price − deposit. LTV = mortgage ÷ property price × 100.
The monthly payment uses the standard annuity formula: payment = P × r ÷ (1 − (1 + r)^−n), where P is the loan, r the monthly rate and n the number of months. Early payments are mostly interest; later ones mostly capital.
Worked examples
Monthly repayment on a £250,000 mortgage
At 4.5% over 25 years: £1,390 a month, £166,874 interest over the term.
What a 1% rate rise does
The same £250,000 at 5.5% costs £1,535 a month — about £146 more.
25 vs 35 years on £200,000 at 5%
£1,169 vs £1,009 a month. The longer term costs £73,184 more interest overall.
What changes the result?
- Interest rate — the biggest single lever.
- Term — longer lowers the payment but raises total interest.
- Deposit — a bigger deposit lowers the loan and the LTV.
Common mistakes
- Comparing deals by rate alone and ignoring fees.
- Assuming today's rate lasts for the whole term — most fixes end after 2–5 years.
- Confusing LTV with deposit percentage (they add up to 100%).
Frequently asked questions
What does 85% LTV mean?
You're borrowing 85% of the property's value and putting down a 15% deposit.
How much does a 1% rate increase change repayments?
On a £250,000 loan over 25 years, roughly £140–£150 a month at today's typical rates. Use the scenario cards for your figures.
Does a larger deposit lower repayments?
Yes — you borrow less, and a lower LTV can give access to more deals.
What mortgage term should I use?
25–35 years is common. Shorter terms cost less interest but more each month.
Is the rate shown today's market rate?
No. It's an illustrative figure to change to the rate you want to model.