Last updated: October 2026
Your circadian rhythm is your body’s roughly 24-hour internal clock. It tells you when to feel sleepy and when to feel alert, and it is set mainly by light. The fastest way to reset it is a fixed wake time every day, daylight soon after waking, and dim, screen-free evenings.
Below: how your body clock works, signs it’s off, a step-by-step reset plan with realistic timescales, special cases and when to see a GP.
Clocks go back on Sunday 25 October 2026: at 2am the time becomes 1am. Lighter mornings are good news for your body clock, but darker evenings mean less daylight overall. See our 5-day plan for the clocks going back.
What is a circadian rhythm?
“Circadian” comes from the Latin for “about a day”. Your circadian rhythm is the cycle of physical, mental and behavioural changes your body runs through over roughly 24 hours. Almost every living thing has one. It does far more than decide when you sleep: it also times hormone release, body temperature and metabolism, so your body is ready for the day before you get up.
The 2017 Nobel Prize in Physiology or Medicine went to Jeffrey Hall, Michael Rosbash and Michael Young for working out how the clock ticks. In fruit flies, they found a gene whose protein builds up in cells overnight and breaks down by day, a self-sustaining daily loop. Human cells work on the same principles.
How your body clock works
Tissues and organs throughout your body have their own clocks, but they are kept in time by a master clock in the brain: a group of nerve cells called the suprachiasmatic nucleus (SCN). It is wired to your eyes, so light is its strongest signal.
- Light and dark have a bigger effect on your circadian rhythm than anything else.
- Melatonin: in the evening the SCN prompts the brain to release more melatonin, the hormone that signals it’s time to sleep. Bright evening light holds it back.
- Core body temperature: it falls at night, reaching its lowest point a few hours before you usually wake. That low point is your sleepiest time, one reason the early hours are so hard on a night shift.
- Cortisol: peaks shortly after you wake. Read more in how to lower cortisol naturally.
- Other cues: meal times, physical activity, temperature, stress and your social life also nudge the clock, but more weakly than light.
Why daily cues matter: left to itself, the human body clock runs slightly long, averaging about 24.2 hours in a landmark study. Without morning daylight to nudge it earlier, most of us would drift a little later every day.
Circadian rhythm vs sleep cycle vs body clock
| Term | What it means | Length |
|---|---|---|
| Circadian rhythm | The daily cycle of sleepiness, alertness, hormones and temperature | About 24 hours |
| Body clock | The everyday name for the system that drives your circadian rhythm, led by the SCN in the brain | About 24 hours |
| Sleep cycle | The stages of light, deep and REM sleep you move through, several times a night | Less than 2 hours, repeating |
| Ultradian rhythm | Any biological rhythm shorter than a day; sleep cycles are an example | Minutes to hours |
| Chronotype | Whether your clock naturally runs early (lark) or late (night owl) | Your personal timing |
Your circadian rhythm decides when you feel sleepy; sleep cycles describe what happens once you are asleep. To time your bedtime around full sleep cycles, try our sleep calculator. If you naturally come alive at 11pm, our guide for the night owl covers chronotypes in depth.
Signs your circadian rhythm is off
When your body clock and your daily timetable don’t match, the usual signs are:
- You can’t fall asleep at the time you want to, but drop off easily much later
- You wake in the night or much earlier than you’d like
- You struggle to wake up and feel groggy for hours
- You feel sleepy in the day and wide awake late at night
- Your sleep times swing a lot between workdays and weekends
Many of these overlap with plain short sleep, so it helps to read about sleep deprivation too. If you feel tired all day as the nights draw in, see why you’re so tired in winter.
How to reset your circadian rhythm: a step-by-step plan
This plan uses your body clock’s biggest cues. The first two steps do most of the work.
| When | What to do | Why |
|---|---|---|
| Every day | Pick one wake time and stick to it, weekends included (within about an hour) | A fixed wake time anchors everything else |
| Within an hour of waking | Get outside for 20 to 30 minutes, even when it’s cloudy, or sit by a bright window | Morning light moves your clock earlier |
| Breakfast | Eat at a regular time each morning | Meal timing is a secondary clock cue |
| Daytime | Be active, ideally outdoors, and keep any nap short | Activity and daylight build sleep pressure for the evening |
| 6 hours before bed | Last caffeinated drink | Caffeine even 6 hours before bed can disturb sleep |
| Early evening | Have your main meal and any hard exercise earlier in the evening, not right before bed | Late big meals and workouts can keep you alert |
| Last 1 to 2 hours | Dim the lights, put screens away for the final hour, no alcohol | Bright evening light holds back melatonin |
| Bedtime | Go to bed when sleepy, around the same time each night, in a dark, quiet room | Regular timing keeps your clock stable |
Fix your wake time first. It’s easier to control than when you fall asleep, and bedtime follows. See how to wake up early.
Make light work for you. Outdoor daylight is usually much brighter than indoor lighting, even on a grey morning. In the evening, use lamps rather than overhead lights. Whether tinted lenses add anything is covered in do blue light glasses work?
Watch caffeine timing. In one study, a strong dose of caffeine 6 hours before bed still cut sleep compared with a placebo. Our guide to caffeine and anxiety has tips for cutting down.
Build a wind-down routine. A bath, reading or a warm caffeine-free drink in the last hour tells your brain the day is ending; see our sleep hygiene guide. Our Magnesium Glycinate Sleep Complex combines magnesium bisglycinate and citrate with glycine, L-theanine, chamomile and passionflower in a caffeine-free berry drink. Magnesium contributes to the normal functioning of the nervous system and to the reduction of tiredness and fatigue. To be clear, no supplement resets your body clock: light and timing do that. See magnesium for sleep for what the research shows.
How long does it take to reset your circadian rhythm?
Expect days to weeks, not hours. Jet lag research gives a rule of thumb:
- Moving earlier is slow. Researchers advise moving your sleep schedule earlier by no more than an hour a day, and night owls by about half an hour.
- Moving later is easier, because your clock naturally runs a little longer than 24 hours.
So if you currently fall asleep at 1am and want to sleep at 11pm, plan on at least 4 days of 30-minute steps. Big weekend lie-ins undo the progress.
Can you reset your circadian rhythm in one day?
Not fully. You can make a strong start in a day, but your clock only moves part of the way each day. Staying up all night to “reset” just adds sleep loss, so we don’t recommend it.
Does morning sunlight really work?
Morning sunlight is a huge social media trend. The science is sound, with caveats.
- Timing matters. Light soon after your body’s temperature low point (in the morning) moves your clock earlier. Light in the late evening and first part of the night moves it later.
- Natural light pulls the clock earlier. In a US camping study with only natural light, people’s internal clocks shifted earlier to line up with sunrise and sunset. Night owls shifted most.
- More daylight goes with better sleep. In over 400,000 UK Biobank adults, each extra hour spent outdoors in daylight was linked with finding it easier to get up, feeling tired less often, fewer insomnia symptoms and an earlier chronotype. This is observational, so it shows a link rather than proof of cause.
- UK sleep experts agree. The British Sleep Society concluded that sleep and circadian health benefit from natural daylight in the morning.
The caveats: there’s no magic number of minutes, and never stare at the sun. A 20 to 30 minute walk within an hour of waking is a realistic target. Pair it with our morning routine for energy.
Shift work, jet lag, clock changes, teenagers and winter
Shift work
Night and early shifts work against your body clock, often bringing poor sleep, digestive problems and fatigue. The Health and Safety Executive suggests keeping lights bright at work to stay alert, using blackout blinds or an eye mask to sleep in the day, taking a short sleep before your first night shift, and keeping to a routine once you find one that works. Full plan: shift work and sleep.
Jet lag
The NHS says jet lag usually improves within a few days. Get outside in daylight at your destination, switch to local sleep times as soon as you can, and only sleep at night. Flying east is usually harder because your clock has to move earlier. See our full jet lag guide.
When the clocks change
In the UK the clocks go back at 2am on Sunday 25 October 2026 and forward again at 1am on Sunday 28 March 2027. The British Sleep Society found that enforced clock changes, especially the spring change, are bad for sleep and circadian health, and recommends ending them. Shifting your routine gradually in the days around the change helps. Our clocks go back guide has a 5-day plan.
Teenagers
Teenagers really are wired to sleep later: research shows sleep timing shifts later through the teens, through a mix of biology and lifestyle. Morning daylight, a steady wake time at weekends and phones out of the bedroom at night help. A teenager who simply can’t fall asleep until the early hours, night after night, should see a GP.
Winter and light boxes
Short, dark days give your body clock a weaker signal, and the NHS says seasonal affective disorder (SAD) is thought to be linked to reduced daylight in winter. A light box can mimic morning daylight, often for 20 to 30 minutes. The NHS advises one that is bright enough (10,000 lux is standard), UV-free and UKCA or CE marked, and to check with your GP first if you have an eye condition or take medicines that cause light sensitivity. Read more about SAD and SAD lamps, and don’t forget vitamin D in winter, which the NHS says everyone should consider taking in autumn and winter.
When it’s a circadian rhythm disorder
Circadian rhythm sleep-wake disorders happen when your body clock consistently doesn’t match the sleep times you need. There are six types:
- Delayed sleep-wake phase disorder: you can’t fall asleep until very late but sleep well if allowed to wake late. It often starts in the teens and is easily mistaken for insomnia.
- Advanced sleep-wake phase disorder: very early sleepiness and waking, more common in older adults.
- Irregular sleep-wake rhythm disorder: broken sleep spread through the day and night, most often seen with dementia.
- Non-24-hour sleep-wake rhythm disorder: sleep times drift around the clock; rare, and can follow loss of vision.
- Jet lag disorder and shift work disorder.
Treatment for delayed sleep phase usually combines scheduled sleep and wake times, bright light therapy and carefully timed melatonin. In the UK, melatonin is prescription-only, so you’d need to see a GP or specialist. Our guide to melatonin in the UK explains why and what the alternatives are.
See a GP if your sleep timing is affecting work, school or relationships, if a few weeks of the plan above hasn’t helped, if you’re very sleepy in the day (especially when driving), or if poor sleep comes with low mood.
Circadian rhythm and your health
In the short term, a disrupted body clock can leave you drowsy, less coordinated and finding it harder to focus and learn.
Over the long term, researchers have linked chronic sleep loss and constantly shifting rhythms with higher rates of obesity, diabetes, mood disorders, heart and blood pressure problems and some cancers. In a UK Biobank study of nearly 89,000 adults, people with the most irregular sleep-wake patterns had a higher risk of death over about seven years than those with typical patterns.
These are mostly observational findings: they show links, not that a late night now and then will harm you. People with irregular sleep may differ in other ways too, such as their jobs or health. The practical message is reassuring: a regular routine with plenty of daylight is a simple, free habit that supports both sleep and wellbeing.
Related guides
- A simple night routine that keeps your body clock steady.
- For why long lie-ins can leave you groggy, see oversleeping: causes and effects.
- Deep sleep vs REM vs core sleep.
- Can you catch up on lost sleep at the weekend?
- Wondering what time to aim for? See the best time to sleep and wake up.
- ADHD and sleep, where a late body clock is very common.
- Tired but wired at night, often a sign of a late body clock.
- See our guide to SAD lamps for how bright morning light is used to support your body clock in winter.
- Blocking light at night is easier with blackout blinds or a mask: see do sleep masks work?
- For a step-by-step plan with times, see how to fix your sleep schedule.
FAQs
What is a circadian rhythm in simple terms?
It is your body’s internal 24-hour clock. It makes you sleepy at night and alert in the day by timing hormones like melatonin and cortisol and your body temperature, and it is set mainly by light.
How do I reset my circadian rhythm fast?
Wake at the same time every day, get outside in daylight within an hour of waking, stop caffeine about 6 hours before bed and keep evenings dim and screen-free. Shift your sleep times by 30 to 60 minutes a day.
Can you reset your circadian rhythm in one day?
Not fully. Your body clock moves earlier by about an hour a day at most, so a big change takes several days. Pulling an all-nighter usually adds sleep loss rather than resetting your clock.
What is the best time to sleep for your circadian rhythm?
There is no single best time. What matters most is a regular schedule that gives you enough sleep before a fixed wake time, with bedtime in the dark hours of the evening rather than the early morning.
Is a circadian rhythm the same as a sleep cycle?
No. Your circadian rhythm is the roughly 24-hour cycle that decides when you feel sleepy. Sleep cycles are the shorter stages of light, deep and REM sleep that repeat several times each night.
Can melatonin reset my circadian rhythm?
Timed melatonin is used to treat some body clock disorders, but in the UK it is prescription-only, so speak to a GP. The NHS doesn’t recommend it for jet lag because there isn’t enough evidence.
Can supplements reset your body clock?
No. Light and regular timing reset your body clock. A supplement can be part of a calm evening routine, but it won’t move your clock.
Sources
- National Institute of General Medical Sciences. Circadian rhythms fact sheet.
- The Nobel Prize. The Nobel Prize in Physiology or Medicine 2017: press release.
- Czeisler CA et al (1999). Stability, precision, and near-24-hour period of the human circadian pacemaker. Science.
- Skubic C et al (2025). Circadian biomarkers in humans: methodological insights into the detection of melatonin and cortisol. Biomolecules.
- Eastman CI, Burgess HJ (2009). How to travel the world without jet lag. Sleep Medicine Clinics.
- Wright KP et al (2013). Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology.
- Burns AC et al (2021). Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes. Journal of Affective Disorders.
- Crawford MR et al (2025). The British Sleep Society position statement on Daylight Saving Time in the UK. Journal of Sleep Research.
- Drake C et al (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine.
- Crowley SJ et al (2007). Sleep, circadian rhythms, and delayed phase in adolescence. Sleep Medicine.
- Kim JH et al (2022). Circadian rhythm sleep-wake disorders in older adults. Sleep Medicine Clinics.
- Barnes KA (2025). Delayed sleep-wake phase disorder. JAAPA.
- Cribb L et al (2023). Sleep regularity and mortality: a prospective analysis in the UK Biobank. eLife.
- NHS. Jet lag.
- NHS. Seasonal affective disorder (SAD).
- NHS. Vitamin D.
- NHS. About melatonin.
- NHS Every Mind Matters. How to fall asleep faster and sleep better.
- Aneurin Bevan University Health Board (NHS Wales). Snooze through winter: simple habits for restful nights.
- Health and Safety Executive. Advice for shift workers.
- GOV.UK. When do the clocks change?
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex.
