Sleep cycle calculator
Find the best time to go to bed — or to set your alarm — so you wake up between sleep cycles instead of in the middle of deep sleep. Pick a mode, enter a time, and get results instantly.
Go to bed at one of these times
To wake up at 7:00 AM, go to bed at 11:15 PM: 5 cycles, 7.5 hours of sleep.
Tap a time to choose it for copying or your calendar. All times include 15 min to fall asleep.
How the sleep calculator works
Sleep isn't one long, even state. Through the night your brain repeats cycles of roughly 90 minutes, moving from light sleep into deep sleep and then into REM sleep, where most dreaming happens. A typical night has four to six of these cycles.
How you feel when the alarm rings depends a lot on where in a cycle it catches you. Woken from deep sleep, you get sleep inertia: that heavy, foggy feeling that can last half an hour or more. Woken from light sleep near the end of a cycle, getting up is much easier.
So the calculator counts in whole cycles. To find a bedtime, it starts from your wake-up time, subtracts complete 90-minute cycles, and then subtracts the time it takes you to fall asleep. To find a wake-up time, it does the same in reverse.
Light sleep
You drift off, your heart rate slows and your body temperature drops. It's the easiest stage to wake up from.
Deep sleep
Slow-wave sleep for physical recovery. It's most common early in the night and the hardest stage to wake up from.
REM sleep
Vivid dreams and memory processing. REM periods get longer towards morning.
Worked example
Say you need to be up at 6:30 a.m. and it usually takes you about 15 minutes to fall asleep.
Five cycles is 7 hours 30 minutes. Counting back from 6:30 a.m. gives 11:00 p.m., and taking off 15 minutes to fall asleep means you should be in bed by 10:45 p.m. Six cycles (9 hours) means getting into bed at 9:15 p.m.
If 10:45 p.m. isn't realistic tonight, going to bed at 12:15 a.m. (four cycles, 6 hours) will probably feel better than 11:30 p.m., which would likely wake you mid-cycle. Six hours is still short, though, so treat it as an occasional exception rather than a plan.
Assumptions and limits
- Results use an average sleep cycle of 90 minutes. Real cycles vary from about 70 to 120 minutes between people and through the night.
- The time to fall asleep is your own estimate. 10–20 minutes is typical for adults; change the slider if you're usually faster or slower.
- Most adults need at least 7 hours of sleep, which is why 5–6 cycles (7.5–9 hours) are highlighted. Teenagers and children need more.
- This calculator gives general information, not medical advice. If you regularly struggle to sleep, snore loudly, or feel exhausted despite enough sleep, talk to a doctor.
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No more doing sleep maths every night. OwlRoutine is a sleep-cycle smart alarm with a guided wind-down routine and wake-up missions you can't snooze through. Free on iPhone and Android.
Frequently asked questions
What time should I go to bed to wake up at 7 a.m.?
If you take about 15 minutes to fall asleep, go to bed at 9:45 p.m. for six cycles (9 hours) or 11:15 p.m. for five cycles (7.5 hours). Going to bed at 12:45 a.m. still lines up with a cycle but only gives you 6 hours of sleep.
How long is one sleep cycle?
About 90 minutes on average, but it varies from roughly 70 to 120 minutes between people and from one cycle to the next. Early cycles contain more deep sleep, later ones more REM sleep.
How many sleep cycles do I need?
Most adults do best with five or six cycles a night, which is 7.5 to 9 hours of sleep. Sleep medicine guidelines recommend at least 7 hours for adults; teenagers and children need more.
Why do I wake up tired even after 8 hours of sleep?
One common reason is that your alarm goes off during deep sleep, which causes sleep inertia. An irregular schedule, alcohol, caffeine late in the day or a sleep disorder can also leave you tired. If it happens most days, it's worth talking to a doctor.
How long should a nap be?
Either a short power nap of 10–20 minutes or a full 90-minute cycle. Naps of 30–60 minutes often end in deep sleep and leave you groggy. Try to nap before mid-afternoon so it doesn't push back your bedtime.
Is a sleep cycle calculator accurate?
It's a good estimate, not an exact measurement. Your cycles won't all be exactly 90 minutes, so use the results as a starting point, then move your bedtime 15 minutes earlier or later depending on how you feel when you wake up.
What if it takes me a long time to fall asleep?
Set the "time to fall asleep" slider to your usual time and the results will adjust. If it regularly takes you more than 30 minutes, a consistent wind-down routine can help, and if it continues for weeks, talk to a doctor about possible insomnia.
