Hundred SummersMortgage repayment calculator: the whole bill, not just the monthly
The monthly payment is the number everyone asks for; the total interest is the number that should drive the decision. This calculator amortises the loan month by month with the Hundred Summers app's own engine, repayment or interest-only, and shows what the term really costs. Your figures never leave your browser.
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Worked example
Computed when this page was built by the same engine that runs the calculator above, so the figures below and the live tool can never disagree. Change any input above to see your own.
| Inputs | |
|---|---|
| Loan | £250,000 |
| Rate | 4.5% |
| Term | 25 years |
| Repayment type | Capital and interest |
| Results | |
|---|---|
| Monthly payment | £1,390 |
| Total interest over the term | £166,874 |
| Total paid | £416,874 |
| Interest share of what you pay | 40% |
| Interest-only would be | £938 a month |
The next question
Overpay the mortgage or invest the difference? →Mortgage overpayment calculator
Or answer it with everything else: the full Hundred Summers plan connects your pay, pensions, savings, property, tax and spending year by year, and stress-tests them across 500 simulated market histories.
Read the guide
- Your mortgage: how the payment is built, what the term costs, and what a rate change does →Why half of every early payment is interest, what stretching the term to 35 years really costs, the interest-only trap, and how a two-point rate rise moves the monthly figure, with the arithmetic behind each.
Reading the numbers like a lender doesn't
Lenders quote the monthly payment because it's the number that fits a budget; the interest share this calculator shows is the number that fits a life plan. At today's rates a typical 25-year loan pays roughly 40% of everything to the bank, and stretching the term to make the monthly “affordable” moves that share steadily higher. The honest comparison is total cost at equal outlay, which is what the overpayment calculator and remortgage calculator price.
One held rate is also a fiction worth naming: real mortgages reprice at every fix's end, and the years after a cheap fix expires are where budgets break. The full Hundred Summers plan carries your actual mortgages through every projected year (rate changes, overpayments, redemption and the payment-free years after) inside the same projection as your pensions and savings, so the “pay it off or invest” question gets answered on your whole position.