Daylight saving time and sleep: how your body clock adjusts

On Sunday, 25 October 2026, clocks across the EU and the UK go back one hour: at 3:00 they return to 2:00. The United States and Canada follow a week later, on 1 November. On paper it is a free hour. For your body it is something else. The link between daylight saving time and sleep is closer than a small jump on the clock face suggests, because your internal clock does not recognise daylight saving time. It follows light, meals and habit.

This article explains why your body clock does not simply jump along, why the autumn change is easier than the one in spring, how much the hour really matters, and how to get through it well.

What happens when the clocks go back

The hour between 2:00 and 3:00 happens twice. If you normally get up at 7:00, you may be awake at 6:00 new time on Sunday, because your body is still on old time. In the evening, darkness arrives an hour earlier.

Why your body clock does not simply jump along

In the hypothalamus sits the suprachiasmatic nucleus (SCN), the master clock of the body. Its intrinsic rhythm is about 24.2 hours, not exactly 24, which is why it needs daily time cues (zeitgebers) to reset it: light is by far the strongest, followed by meals, physical activity and social contact. Two hormones make the rhythm tangible. Melatonin, the darkness hormone, begins to rise about two to three hours before your usual bedtime; cortisol, its counterpart, rises during the second half of the night and peaks about 30 to 45 minutes after waking. When the clock on the wall is moved, these rhythms carry on at the old time for a while. The clock change is not a calendar detail. It is a small jet lag for your body clock, without the flight. Your chronotype plays a part too: whether you are more of an owl or a lark affects how easily you absorb the shift.

Autumn is easier than spring, but the evenings get darker

In chronobiology, the October change is considered the easier of the two: a body clock that naturally runs slightly longer than 24 hours stretches more readily to a later schedule than it compresses to an earlier one. In autumn you get to sleep an hour longer; in March you have to get up earlier, against the natural drift. Still, autumn has a catch: darkness falls an hour earlier, abruptly. Less evening light means an earlier darkness signal to the pineal gland, melatonin rises sooner, and some people feel tired in the late afternoon for weeks after the change. That the days are getting shorter overall is seasonal, though, and has nothing to do with the clock change; the clock only shifts which time of day the available light is assigned to. Anyone who commutes in the dark both ways gets almost no daylight on weekdays, even though that is the most important lever.

Light is the strongest time cue

Specialised retinal cells (ipRGCs, containing the photopigment melanopsin) respond particularly to blue light around 480 nanometres and report brightness directly to the SCN. The differences are larger than the eye suggests: sunshine outdoors delivers 10,000 lux and more, an overcast sky still 3,000 to 5,000 lux, an office only around 500 lux. Fifteen to 30 minutes outside in the morning is therefore the most effective signal for stabilising the clock after the change. One subtlety for the first days: if you are awake at six instead of seven on Sunday, do not head straight out into the dawn, because very early light pulls the clock even further forward; better to get into daylight at your usual wake time on the new clock. In the evening the opposite applies: dim the lights from about 8 pm, warm light around 2,700 kelvin, ideally below 50 lux. Chang et al. (2015, PNAS) showed that four hours of reading on a brightly set tablet on five consecutive evenings delayed melatonin onset by around 1.5 hours, left participants sleepier the next morning and reduced REM sleep. That is an extreme case, but it shows the direction.

How much does the hour really matter?

Every year we read that the clock change makes people ill. The data are more sober. In our own online survey “How does Austria sleep?” (University of Salzburg, 2019, around 1,000 participants, not representative), 87 % said the change affected them not at all or only slightly. Most people adjust within a few days, some take longer; there is no fixed cut-off such as “48 hours”. How strongly someone feels the hour depends on chronotype, daily routine and how stable their sleep was beforehand.

At the population level there are measurable but small effects, and they mainly concern spring: a meta-analysis of seven cohort studies (Manfredini et al., 2019) found a roughly 5 % higher relative risk of heart attack in the week after the switch to daylight saving time; after the autumn change, no increase was detectable. A review of 157 studies from 36 countries (Steponenaite et al., 2026) concludes that the consequences of clock changes are not uniformly negative: after the autumn change, the evidence points to longer sleep and fewer workplace accidents. We argued for this balanced view back in 2020 (Blume & Schabus, Clocks & Sleep): take the effects seriously, but state their size instead of fanning fear. From a sleep-research perspective, the twice-yearly switch could be dispensed with, and most scientific societies favour permanent standard time; how large the health difference between the models would actually be remains open.

Daylight saving time and sleep: your plan for the week

The plan is unspectacular but effective, because it works with the time cues rather than against them. For most people it is enough to keep a stable rhythm and get into daylight in the morning. If you know from experience that the change hits you hard, you can pre-empt it: from Wednesday or Thursday, move your bedtime and wake time later by 10 to 15 minutes each day; by Sunday you will have absorbed most of the hour. This is a general chronobiological recommendation, not a sleep² study.

Keep your wake time: get up at the new time on Sunday, even if you are awake earlier, and go straight into daylight. Sunday is not the day to sleep in. Anyone who extends the free hour by two more builds in social jetlag. Wittmann, Roenneberg and colleagues (2006) define it as the difference between weekday and weekend sleep midpoints; in observational data it is associated with overweight (Roenneberg et al., 2012), depressive symptoms and cardiometabolic risk markers. As a rule of thumb, keep weekend deviation to about an hour at most.

Set a caffeine cut-off: caffeine has a half-life of around five hours (two to ten, depending on the person), so a coffee at 2 pm can still be half active at 7 pm. In a double-blind study, Drake et al. (2013) found that 400 mg of caffeine six hours before bed cut total sleep time by more than an hour. Add dimmed light from 8 pm and a fixed wind-down routine; more building blocks are in our article on how to improve your sleep. Regularity matters beyond this one weekend: Windred et al. (2024, Sleep, UK Biobank, around 61,000 people measured with actigraphy) found that very regular sleep was associated with a 20 to 48 % lower mortality risk, independent of sleep duration.

Who feels the hour most

Young children often have a very stable body clock and wake an hour early after the change; for them the gradual shift in 10- to 15-minute steps is particularly worthwhile. Teenagers already have a later melatonin rise because of the phase delay of puberty, so the autumn change is likely to suit them. Anyone on night shift that night has an extra hour on duty and often the sharpest break in rhythm; morning light and fixed sleep windows in the days that follow help most. People who already struggle to fall or stay asleep may react more sensitively. The clock change does not cause a sleep disorder, but it can temporarily amplify existing patterns; if problems persist for weeks, a medical assessment is advisable. Why sleep quality matters more than duration is the subject of a separate article.

What sleep² shows you this week

In the sleep² app you can see your bed and wake times, your regularity across the week and how your recovery develops in the days after the change. Measurement is objective, based on the cardiac signal of the Polar sensor (PPG on the upper arm or ECG from the chest strap), from which sleep² derives sleep stages and wake time. What matters is the trend, not a single night: an unsettled night around the change is normal, as long as the pattern settles again within a few days.