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Mortgage term length (UK): how it changes your monthly payment and total interest

A longer mortgage term usually lowers monthly payments but increases total interest. Here’s the practical trade-off with a small example.

Published: 17/03/2026 • Last verified: 17/03/2026

The short answer

If you keep the loan amount and interest rate the same, a longer mortgage term usually means a lower monthly payment — because you’re spreading the repayments across more months.

But the trade‑off is that you usually pay more interest overall, because the interest is charged over a longer period.

A tiny example

Illustrative example (repayment mortgage, ignoring fees and assuming the rate stays at 4%):

  • Mortgage: £200,000
  • Interest rate: 4% a year

If you compare a 25‑year term to a 15‑year term (same loan, same rate):

  • 25 years: monthly payment ≈ £1,055.67; total interest ≈ £116,702
  • 15 years: monthly payment ≈ £1,479.38; total interest ≈ £66,288

So the 25‑year term is about £424/month cheaper, but costs about £50,414 more in interest overall.

Use the mortgage repayment calculator to run your exact numbers.

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