The clocks go back. Your body clock doesn’t.

A westbound flight without leaving home

At 2am on Sunday 25 October 2026, British Summer Time ends and the clocks fall back to 1am. Most of us file this under good news: an extra hour in bed, no effort required.

Your body keeps a different record. Almost every cell runs on an internal clock that spent the summer tuned to longer, brighter days, and none of them reset at 2am. For several days your alarm, your meals and your evening light all land an hour away from where your biology expects them. It is the jet lag of a short westbound flight, without the holiday at the other end.

How long that lasts varies more than most people realise. Your genes set where your clock starts, your blood shows how well you are coping with shorter days, and a handful of habits decide how quickly you catch up.

This article explains:

Why your body clock lags behind your phone

A master clock in the brain, the suprachiasmatic nucleus, keeps your body on a cycle of roughly 24 hours. It times the evening rise in melatonin, the morning peak in cortisol, the fall in core temperature and the arrival of hunger. Smaller clocks in the liver, gut and muscle follow its lead.

That master clock never reads the time from your phone. It sets itself from outside cues, which scientists call zeitgebers, or “time givers”.

When the clocks go back, every one of those cues lands an hour later on your body’s schedule. Your clock can shift, but often by less than an hour a day. Until it catches up, you live with mild jet lag: awake too early, sleepy too soon and hungry at odd times.

Why autumn feels gentler than spring

Your body clock naturally runs slightly longer than 24 hours, so stretching a day is easier than shortening one. That makes the autumn change gentler on average than the spring one. Gentler does not mean painless: early waking, broken sleep and an afternoon slump are common in the first week, and darker evenings remove some of the light your clock relies on. If the tiredness outlasts the first week, our guide to persistent tiredness explains what to check.

Lark or owl? Your genes set the starting point

Whether you wake naturally at 6am or come alive at 11pm is partly written in your DNA. This trait, your chronotype, comes from many genes that build and tune the molecular clock inside your cells, including PER2 and PER3. Research consistently shows that chronotype is substantially inherited, which is why willpower alone rarely turns an owl into a lark.

Chronotype matters most when the clock moves against you. A study that tracked junior doctors’ sleep and scored their genes for early or late tendencies found that genetic larks adjusted to the spring change within days, while genetic owls stayed out of step for most of the week. After the autumn change, the study found no clear difference. Your chronotype still decides where to focus your effort.

What your DNA report shows

Four reports in the Stride gene report bear directly on the clock change.

Five habits that help your body clock catch up

1. Fix your wake-up time

A consistent wake time anchors every other rhythm in your day. From Sunday, pick a wake time on the new clock and hold it every day, weekends included. Resist turning Saturday into a late night just because the clock gives you room. Sleep through the extra hour and you start the week slightly ahead.

2. Get daylight early, and later if you need it

Daylight within an hour of waking tells your master clock that the day has begun. If you are a lark now waking too early, add a second dose in the late afternoon: later light nudges your clock later and stops the drift towards a 9pm bedtime.

3. Dim the lights in the evening

Bright overhead lights and screens late in the evening delay the melatonin rise that prepares you for sleep. In the last hour before bed, switch to lamps, lower screen brightness and leave work email until morning.

4. Keep coffee to the morning

Caffeine has a half-life of around five hours in most adults, so half of a 3pm coffee can still be circulating at 8pm. Your genes change the maths. CYP1A2 sets how fast your liver clears caffeine, and ADORA2A sets how sensitive your brain is to it. A slow metaboliser with a sensitive ADORA2A type may need a noon cut-off; a fast metaboliser may manage mid-afternoon.

5. Eat at your usual times

Eat breakfast, lunch and dinner at your normal times on the new clock, so the clocks in your gut and liver reset alongside your brain. Avoid large late meals, which keep digestion busy when your body should be winding down.

What your blood and gut add

Your DNA sets your tendencies. Your blood and gut show how your body is coping now.

Cortisol: timing changes the result

Cortisol peaks shortly after waking and falls through the day, so a blood reading depends heavily on when it is taken. A sample drawn at 8am in the first week of GMT reflects what your body still treats as 9am. If you track cortisol over time, keep your sample time consistent relative to waking, and wait a week after the clock change before you test.

Vitamin D: the real autumn story

From October to March, UK sunlight is too weak for your skin to make meaningful amounts of vitamin D, and the NHS advises everyone to consider a daily supplement through those months. Research links lower levels with poorer sleep quality. Your VDR result adds context on how your body uses vitamin D, but only a blood test shows your actual level.

Your gut makes the raw materials for sleep

Gut bacteria help produce and regulate serotonin, which your body converts into melatonin each evening, and they influence GABA, the brain’s main calming messenger. Your gut microbes also keep their own daily rhythm, set by your mealtimes, which is one more reason to keep meals regular while you adjust.

How to adjust to the clocks going back: a day-by-day plan

Most people feel back to normal within a week. If you are still struggling after two weeks, or your sleep was poor before the clocks changed, speak to your GP. Our guide to poor sleep covers the biological causes worth investigating.

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