How mortgage interest adds up

On a repayment mortgage every monthly payment splits into interest (charged on the current outstanding balance) and capital (which reduces the balance). Early in the term interest dominates — often 60-80% of each payment in year 1. By the final years, the split flips and capital dominates. Total lifetime interest on a 25-year £250,000 mortgage at 4.85% is roughly £183,000 — comparable to the loan itself. For sensitivity to rate rises, see the mortgage stress test calculator, which shows your payment at +1pp, +2pp, +3pp and an 8% worst-case.

Rate vs term — which cuts interest more?

A lower rate always reduces lifetime interest — but to access it mid-term you usually have to switch lender, and the total cost of remortgaging (solicitor fees, product fee, valuation, any ERC) eats into the headline rate saving. A shorter term reduces lifetime interest even more aggressively, because the balance falls faster. On the same £250,000 loan, dropping from 25 to 20 years at the same 4.85% rate cuts total interest from about £182,000 to £141,000 — a £41,000 saving — but monthly payment rises by about £190. See the overpayment calculator for the same effect via overpayments without formally shortening the term.

Frequently asked questions

What's a typical UK mortgage interest rate in 2026?

Mainstream 5-year fixed residential sits in the 4.15-5.65% range depending on LTV band in October 2026. See the LTV calculator for current band ranges.

Does interest get charged daily or monthly?

UK mortgages are almost all calculated on daily interest with monthly billing. Overpayments reduce interest from the day they're received, not the next billing cycle.

Is interest-only cheaper?

Monthly, yes — you only pay the interest. Lifetime, no — the balance never reduces, so total interest paid is far higher. Mainstream residential interest-only is largely restricted to high-net-worth cases.

Related calculators

Last reviewed: 1 October 2026.