Mortgage repayment calculator
Enter the loan, the rate and the term to see the monthly repayment, the total interest, and what a rate rise would do to it.
How this is calculated
This is the standard repayment mortgage calculation. Each payment covers the interest accrued that month, and the remainder reduces the balance.
Early on almost all of the payment is interest, which is why the balance seems to barely move in the first few years. The proportion shifts steadily towards capital as the balance falls.
The comparison line shows the same loan two percentage points higher, because that is roughly the shock a household faces coming off a fixed deal into a higher rate market.
Buildings insurance, service charges, ground rent and any product fee added to the loan are not included.
Rates used · 2026/27
| Standard term | 25 to 35 years |
| Interest-only | not covered here |
| Product fees | often £999 to £1,499, sometimes added to the loan |
| Stress test | lenders test affordability above your actual rate |
Last checked July 2026. Source: HMRC and gov.uk.
Worked example
Borrowing £240,000 over 30 years at 4.5% costs £1,216.04 a month. Across the full term that is £437,776 repaid, so £197,776 of interest, almost as much again as the amount borrowed. At 6.5% the same loan would cost £1,516.96 a month, £301 more.
Common questions
Why is the total interest so large?
Because it accrues on a big balance for a long time. Over 30 years the interest on a typical mortgage can approach the amount borrowed.
Does a longer term save me money?
No. It lowers the monthly payment and increases the total paid, because you are borrowing the same money for longer.
What happens when my fixed rate ends?
You move to the lender standard variable rate unless you remortgage. The two point comparison above shows roughly what that shift can look like.
Is this the same as interest only?
No. On interest only you pay only the interest and the balance never falls, so the monthly cost is lower but you still owe the full amount at the end.