Ten years into a 25-year mortgage you have repaid a quarter of it
A £250,000 loan at 5% costs £1,461 a month. After a decade of paying that, £184,811 is still owed. Amortisation front-loads interest, and above 6.5% you repay the price of the house a second time.
- Source
- Standard amortisation, computed from first principles
- Period
- £250,000 over 25 years, capital repayment
- Published
- August 10, 2026
- Built with
- Databoat
131.54%
of the purchase price paid a second time, in interest alone
8%
- 3%42.26%
- 4%58.35%
- 5%75.38%
- 6%93.29%
- 7%112.03%
- 8%131.54%
Each line is one interest rate. The curves barely bend for the first decade — early payments are almost entirely interest, so the balance moves slowly no matter what you pay.
The shape is identical at every rate. Only the steepness of the late years changes.
The loan, then the interest on top. The second bar is the part nobody quotes.
- 8%£328,862
- 7%£280,084
- 6%£233,226
- 5%£188,443
- 4%£145,878
- 3%£105,658
Three points of rate nearly triples what the house costs you.
| After 5y | After 10y | After 15y | After 20y | |
|---|---|---|---|---|
| 3% | £213,764 | £171,671 | £122,775 | £65,977 |
| 4% | £217,762 | £178,398 | £130,336 | £71,653 |
| 5% | £221,450 | £184,811 | £137,790 | £77,445 |
| 6% | £224,830 | £190,880 | £145,086 | £83,317 |
| 7% | £227,905 | £196,583 | £152,181 | £89,234 |
| 8% | £230,685 | £201,908 | £159,036 | £95,162 |
Read across a row and the loan hardly moves until the middle. Teal is paid down, amber is still owed.
Method
No external data. A £250,000 capital repayment mortgage over 25 years, and the standard amortisation formula, computed from the interest rate alone.
Databoat derived twelve columns from one: the monthly rate, the compounding factor, the monthly payment, the total repaid, the interest, and the outstanding balance at five-year intervals. Every figure on this page comes out of the rate in the left-hand column.
Two things fall out that people consistently get wrong. Amortisation is front-loaded: at 5%, ten years and £175,000 of payments into a 25-year term, £184,811 of the original £250,000 is still outstanding — about a quarter of the capital repaid, for 40% of the term served. And above 6.5% the interest exceeds the purchase price, so the house is bought twice.
This models a single fixed rate for the whole term, which almost nobody has in the UK — fixes typically run two to five years before reverting or being remortgaged. Read each row as "what this loan costs if this rate held", not as a forecast. Fees, overpayments and rate changes are not modelled.
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