How to Reset Your Body Clock: Circadian Rhythm and Melatonin

Last updated: October 2026

A body clock that has drifted out of step with your day is fixable, and usually faster than people expect. The tools are not complicated: light at the right times, darkness at the right times, and a wake time that does not move. This guide explains what the circadian rhythm and melatonin actually are, and the steps that reset them.

What is the circadian rhythm?

The circadian rhythm is the internal clock, running on a cycle of roughly 24 hours, that tells your body when to be sleepy, alert, hungry and warm. It is kept by a cluster of nerve cells called the suprachiasmatic nucleus in the hypothalamus, which sits just above the point where the optic nerves cross, so its main time signal is the light reaching your eyes.

That wiring is the whole trick to resetting it. Morning light tells the clock the day has started and pulls everything earlier; bright light in the late evening tells it the day is still going and pushes everything later. The clock also drives a nightly drop in core body temperature, which is one reason a cool, dark bedroom makes sleep come more easily.

What is melatonin and what does it do?

Melatonin is the hormone the pineal gland releases in response to darkness, signalling to the rest of the body that night has arrived. Levels start rising a couple of hours before your usual bedtime, peak in the early hours and are switched off by morning light. It does not knock you out like a sedative; it opens the gate that lets sleep happen.

Two practical points follow. First, evening screens and bright overhead lighting delay the rise, which is why the last two hours before bed matter more than any supplement. Second, melatonin production declines with age, which is one reason sleep often gets lighter in later life. In the UK melatonin is a prescription-only medicine, usually prescribed short-term for adults over 55, so it is not something to self-dose from the internet; the NHS advises speaking to a GP if sleep problems persist beyond a few weeks.

How do you reset your body clock?

Anchor the wake time first: get up at the same time every day, weekends included, because the clock sets itself by when the day starts, not when it ends. Everything else supports that anchor.

Light does most of the heavy lifting. Get outside, or at least to a bright window, within an hour of waking; in the evening, dim the main lights and keep screens low and warm for the last two hours. The clearest demonstration of how strongly light rules the clock is a University of Colorado study by Wright and colleagues, published in Current Biology in 2013, which found that one week of camping without artificial light re-synchronised participants' body clocks to the sun, with melatonin onset shifting around two hours earlier. You do not need a tent; you need bright mornings and dim evenings.

Move gradually. Shift bedtime and wake time by 15 to 30 minutes a day towards the schedule you want rather than making one big jump, which the clock resists. Keep naps to 20 minutes and before 3 pm so they do not drain the pressure to sleep at night, and hold the routine steady for one to two weeks; consistency is what convinces the clock the new schedule is real. Our guides on falling asleep fast and staying asleep all night cover the two ends of the night, and if you are catching up after a run of short nights, the sleep debt guide explains why earlier bedtimes beat weekend lie-ins. Shift workers have a harder version of the same problem, covered in our night shift sleep guide.

What foods help melatonin production?

Tart cherries are the best-evidenced dietary source of melatonin, and small trials have linked tart cherry juice with modest improvements in sleep time. Beyond that, foods rich in tryptophan (turkey, milk, eggs, oats) and magnesium (nuts, seeds, leafy greens) supply the raw materials the body uses to make melatonin and serotonin.

Keep the claims in proportion: no food will overpower a bright screen at midnight. Food choices are a supporting act; light and timing are the leads. The same goes for caffeine, which blocks the sleep-pressure chemical adenosine for six hours or more, so an afternoon cut-off protects the schedule you are trying to build.

How do you adjust when the clocks go back?

The clocks go back one hour at 2 am on the last Sunday in October, which in 2026 is Sunday 25 October, when British Summer Time ends. It is the easier of the two yearly changes, but for a few days your body clock runs an hour ahead of the new time, so you feel sleepy earlier in the evening and wake earlier than you want to.

Most adults settle within a few days without doing anything special. If you are sensitive to change, or have young children who would otherwise be up at dawn, move the hour in four 15-minute steps instead of one jump. Here is the plan for someone who usually sleeps from 10 pm to 7 am; move your own times by the same steps.

Shift your evening wind-down later along with your bedtime, keeping normal lighting until then, because evening light helps push the body clock later. On Sunday and Monday, get outside in daylight soon after waking at the new time to lock it in. If work fixes your weekday alarm, skip the plan and go to bed at your usual time by the new clock from Sunday; the early waking settles within a few days.

Children often feel the change most, waking at what is now 6 am. The same 15-minute steps work for their bedtime, and our guide to the best mattress for kids covers the rest of a good setup.

What changes in the weeks after?

For a few weeks after the change, mornings are lighter and evenings are dark by late afternoon. Dark early evenings can make you sleepy well before bedtime, so keep normal lighting until your usual wind-down rather than settling in for the night at 6 pm.

As the days shorten through November, get outside in the morning or at lunchtime, because daylight is still the strongest signal your body clock receives. When the clocks go forward again in late March, run the same plan in reverse: go to bed and get up 15 minutes earlier each day from the Wednesday before.

What about light summer mornings?

Light summer mornings and evenings pull the clock the other way, waking you at 5 am or keeping you up past midnight. Blackout curtains or a contoured eye mask restore the darkness signal in the morning, and dim, warm lighting after sunset preserves the evening melatonin rise even when it is still bright outside. The room itself is part of the signal: dark, quiet and around 16 to 18 degrees is the environment the clock expects at night.

Does your bed affect your body clock?

Indirectly but meaningfully, because the nightly drop in core temperature is one of the circadian signals for sleep, and a mattress that traps heat works against it. A surface that lets warmth escape helps your body make the temperature drop the clock is trying to schedule.

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Body clock and melatonin FAQs

Last updated: October 2026

How long does it take to reset your body clock?

Around one to two weeks for most schedule drifts, moving 15 to 30 minutes a day with a fixed wake time and bright morning light. As a rule of thumb the clock shifts about an hour a day at best, so a big change such as night-shift work or long-haul travel takes proportionally longer.

Do you get an extra hour of sleep when the clocks go back?

Only if your body lets you take it. On the night itself you can stay in bed an hour longer by the clock, but many people wake at their usual body-clock time, which is now an hour earlier by the new time. Shifting bedtime 15 minutes later on each of the four nights before means the extra hour lands as a normal morning rather than a 6 am wake-up.

How long does it take to adjust when the clocks change?

Most people adjust within a few days, and the autumn change is usually easier than the spring one, because losing an hour of sleep is harder on the body than gaining one. Some people take a week or more; a fixed wake time and daylight soon after waking are the quickest fixes.

Can you buy melatonin in the UK?

Not over the counter. Melatonin is a prescription-only medicine in the UK, usually prescribed short-term for adults over 55 with insomnia. Speak to a GP rather than buying it online, and treat light exposure and a fixed wake time as the first-line fix.

Does pulling an all-nighter reset your sleep schedule?

No. Staying up all night adds sleep debt on top of a shifted clock, and the crash that follows usually lands at the wrong time and makes the drift worse. Shift gradually with a fixed wake time instead; it takes a few days longer and actually holds.

Why do light mornings wake me up so early?

Because morning light shuts down melatonin and signals the start of the day, even at 5 am through closed eyelids and thin curtains. Blackout curtains or an eye mask restore the darkness signal so your clock runs to your schedule rather than the sun's.

What is the best light for sleep in the evening?

Dim and warm. Low, warm-toned lamps in the last two hours before bed let melatonin rise on time, while bright overhead or blue-toned light delays it. Keep screens low, use night mode, and make the bedroom itself as dark as you can.

Sources: Wright et al., Entrainment of the human circadian clock to the natural light-dark cycle, Current Biology, 2013; NHS, Melatonin; Sleep Foundation, Circadian Rhythm; GOV.UK, When do the clocks change?; Sleep Foundation, Daylight Saving Time.