Sleep Cycle Calculator
＋More features: match your own cycle length, or go to bed right now
Recalculate with your own cycle length
Cycle length varies from person to person (roughly 70–110 minutes), so if 90 minutes does not fit you, recalculate with 80 or 100 minutes (the times are taken from the form above).
If I go to bed right now, when should I get up?
Using the current time as the starting point, this suggests wake-up times that fall on a cycle boundary (the cycle length and the time to fall asleep come from the settings above).
Just enter the time you want to wake up and you immediately get three suggested bedtimes that are easy to wake up from. Sleep repeats in cycles of about 90 minutes, so the idea is to wake up at the boundary between cycles. Handy on the nights when you think, “I have to be up at 6 tomorrow — when should I go to bed?”
How to use
- Enter the time you want to wake up (or the time you plan to go to bed).
- Enter roughly how long it takes you to fall asleep (15 minutes is a good default).
- As you type, times matching 6 hours, 7.5 hours and 9 hours of sleep appear below. No button needed.
How it is calculated
- Suggested bedtime = wake-up time − (90 minutes × number of cycles) − time to fall asleep
- Three patterns are shown: 4 cycles (6 hours), 5 cycles (7.5 hours) and 6 cycles (9 hours). Adults are recommended to get at least 6 hours of sleep.
- Example: waking at 6:30 with 15 minutes to fall asleep gives a 5-cycle (7.5-hour) bedtime of 22:45.
Sources and assumptions
- Explanation of the sleep cycle (non-REM and REM sleep repeating in roughly 90-minute cycles): Ministry of Health, Labour and Welfare (Japan), e-Health Net (rest and mental health) (in Japanese). 90 minutes is an average; individual differences of roughly 70–110 minutes are normal.
Assumptions and notes
- Cycle length differs a lot between people, so there is no guarantee that a multiple of 90 minutes will always leave you refreshed. Treat the times as a rough guide.
- What matters most is getting enough sleep and keeping your bedtime and wake-up time the same every day.
- If strong daytime sleepiness or insomnia continues, see a doctor.
Frequently asked questions
Is the 90-minute cycle real?
That non-REM and REM sleep repeat in cycles of about 90 minutes is a well-known physiological phenomenon. However, the cycle ranges from about 70 to 110 minutes depending on the person, and it also changes over the course of a single night. The times here are a guide in the sense of “if your cycle is the average 90 minutes, this is the time”.
Is 6 hours of sleep enough?
Most adults do well on roughly 6 to 8 hours, and the amount needed varies from person to person. Strong sleepiness during the day is a sign you are not getting enough. If you can, pick the 5-cycle (7.5-hour) option or longer.
I go to bed at the suggested time but cannot fall asleep.
A phone screen, caffeine or a very hot bath right before bed all make it harder to fall asleep. Getting into bed when you are not sleepy can also backfire. The standard advice is to get into bed once you feel sleepy, and instead keep your wake-up time constant.