A UK mortgage calculator that shows your monthly repayment, the total interest over the full term and a complete month-by-month amortisation schedule — plus the exact effect of overpaying. It’s for anyone comparing mortgage deals, sizing a deposit, or deciding how much to overpay before committing to a fixed-rate period.
How it works
The tool models a standard UK repayment (capital-and-interest) mortgage. The loan is your property price minus your deposit. The fixed monthly payment comes from the amortising-loan formula:
M = P · r(1+r)ⁿ ⁄ ((1+r)ⁿ − 1)
where P is the loan, r is the monthly rate (annual rate ÷ 12 ÷ 100) and n is the number of months (years × 12). The calculator then simulates each month: it charges interest on the outstanding balance, applies the payment (plus any overpayment) to clear principal, and rolls the balance forward until it reaches zero. Because overpayments go straight to principal, it also runs a no-overpayment baseline and reports the interest saved and months knocked off.
Example
A £300,000 home with a £60,000 deposit gives a £240,000 loan. At 4.5% over 25 years:
- Monthly payment: £1,334
- Total interest over the term: about £160,000
Add a £200/month overpayment and the mortgage clears roughly 4 years and 8 months early, saving around £28,000 in interest.
| Loan | Rate | Term | Monthly payment |
|---|---|---|---|
| £150,000 | 4.5% | 25y | £834 |
| £240,000 | 4.5% | 25y | £1,334 |
| £240,000 | 5.5% | 25y | £1,474 |
| £240,000 | 4.5% | 30y | £1,216 |
Every figure is calculated in your browser — no numbers are uploaded or stored.