40-Year Mortgage UK: Stretched, Trapped, or Smart?
A 40-year mortgage looks like the obvious answer when you're stretched. The interest isn't the trap. It's what the bank can do to you at year 5.
£300,000 mortgage at 5%: term vs total cost
| Term | Monthly | Total cost | Extra vs 25yr |
|---|---|---|---|
| 25 years | £1,754 | £526,200 | baseline |
| 30 years | £1,610 | £579,600 | +£53,400 |
| 35 years | £1,514 | £635,880 | +£109,680 |
| 40 years | £1,446 | £694,080 | +£167,880 |
Stretching to 40 years saves £308 a month and costs £168,000 in extra interest.
Key takeaways
A 40-year UK mortgage is usually a warning sign you have stretched yourself to buy a house you cannot really afford on a 25-year term.
You will renew the rate roughly every 5 years - eight renewals over the full term, eight chances for rate hikes, redundancy or a market crash to break you.
Buying only beats renting if you stay 5 to 7 years, but the 40-year structure pushes you to need to stay much longer to build any equity.
The narrow case where 40 years makes sense: you could comfortably afford a 25-year payment and deliberately choose 40 to free up cashflow you actually invest.