When the clocks go back: what it does to your body clock

On Sunday 25 October 2026, at 2am, the clocks in the UK go back one hour to 1am. British Summer Time ends and we return to Greenwich Mean Time. Most of us think of it as the good clock change: an extra hour in bed.

Your body clock sees it differently. It does not read the clock on the wall. It takes its timing mainly from light, and the clock change moves the hours of light and dark you meet in your day by an hour overnight.

What actually changes

After the change, sunrise and sunset both arrive an hour earlier by the clock. Mornings are lighter for a while, and evenings get dark noticeably sooner. Your alarm, meals, commute and bedtime all shift by an hour against the light outside, and against your internal clock, which was set to the old pattern.

For many people the difference passes in a few days. Some notice it more: waking earlier than they would like, feeling sleepy earlier in the evening, or simply feeling a little out of step for the first week.

Why your body clock takes time to catch up

The body clock runs on a cycle of roughly 24 hours and is kept in time mainly by light, especially light in the morning. It adjusts gradually rather than all at once. A sudden one-hour shift is small, but it still takes the clock a few days to settle, in the same way that a short flight across one time zone can leave you slightly off for a day or two.

Children, older people and anyone who already sleeps at irregular times may notice the change more, simply because their routines and light exposure are less flexible.

The real issue is the dark that follows

The extra hour gets the headlines, but the bigger change is what comes after it. From late October, daylight in the UK is short, and many people now travel to and from work in the dark and spend the daylight hours indoors. Indoors, light levels at the eye are usually far lower than outside, even on an overcast day.

So for many of us, winter means less light during the day and plenty of artificial light in the evening: close to the opposite of the pattern the body clock evolved for.

Simple habits that help the adjustment

These are general suggestions, not medical advice.

• Get daylight early. Time outdoors in the morning, even on a cloudy day, is the clearest timing signal you can give your body clock.
• Keep your wake-up time steady. A consistent time to get up, including at weekends, helps the clock settle faster than lie-ins.
• Go easy on bright light late at night. Dimmer, warmer light in the last hour or two before bed sends a clearer evening signal.
• Give it a few days. Most people adjust within the first week.

If poor sleep carries on for weeks rather than days, speak to your GP.

Why this matters to us

The clock change is a small, twice-yearly reminder of something that is true every day: the light we receive shapes how our bodies keep time. At Sensio BioLabs we study the light people actually receive through the day, indoors and out, and how it relates to how they feel and function. Read more in our guide Circadian lighting explained.