When to go to bed for a wake-up time, or when to wake, counted in 90-minute sleep cycles
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Sleep Calculator counts back from your wake-up time in 90-minute sleep cycles plus about 15 minutes to fall asleep. To wake at 06:30, go to bed at 21:15 for six cycles (9 hours) or 22:45 for five (7.5 hours). The 90-minute cycle is an average, not a fixed length.
Under "I want to", pick Wake up at a time or Go to bed at a time.
Enter the "Time", or press "Going to bed now".
Set "Minutes to fall asleep" (15 is typical) and, if you know yours, the "Cycle length" (90 minutes on average).
Read the times for six, five, four and three cycles; the ones with 7 hours or more of sleep are marked.
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Sleep runs in cycles: light sleep, deep sleep, then REM, and round again, four to six times a night. Waking at the end of a cycle, when sleep is lighter, tends to feel easier than being pulled out of deep sleep. This calculator turns that idea into clock times. Tell it when you need to wake up and it gives bedtimes for six, five, four or three full cycles; tell it when you are going to bed and it gives the matching wake-up times.
The working is plain arithmetic. Bedtime = wake-up time − cycles × cycle length − time to fall asleep. Wake time = bedtime + time to fall asleep + cycles × cycle length. To wake at 06:30 with 90-minute cycles and 15 minutes to drop off, five cycles (7 hours 30 minutes) means lights out at 22:45.
The 90-minute cycle is an average. Textbook figures put one cycle at roughly 90 minutes on average, commonly anywhere from about 80 to 110 minutes, and cycles change through the night: more deep sleep early on, longer REM periods towards morning (Carskadon and Dement, "Normal Human Sleep: An Overview", Principles and Practice of Sleep Medicine). Your own cycles also vary from night to night. So the times here are a reasonable target, not a promise that you will wake between cycles. If you know your cycles run longer or shorter, change the cycle length. Time to fall asleep defaults to 15 minutes and can be changed too.
How much sleep. The American Academy of Sleep Medicine and the Sleep Research Society recommend that adults sleep 7 or more hours a night on a regular basis (Watson et al., "Recommended Amount of Sleep for a Healthy Adult", Sleep, 2015). Five cycles (7.5 hours) or six (9 hours) meet that; four cycles (6 hours) do not, and the page marks which options fall short. Children and teenagers need more.
This page gives general information and is not medical advice. Long-term trouble falling or staying asleep, loud snoring, or feeling unrested after a full night are worth raising with a doctor. Nothing you enter leaves your browser.
With 90-minute cycles and 15 minutes to fall asleep: 21:15 for six cycles (9 hours of sleep), 22:45 for five (7.5 hours), or 00:15 for four (6 hours). Five or six cycles meet the 7-hour minimum recommended for adults.
No. 90 minutes is an average. A cycle commonly runs from about 80 to 110 minutes, cycles change through the night, and they differ between people and from night to night. Treat the times here as a target; you can change the cycle length if yours is different.
The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 or more hours a night on a regular basis for adults (Watson et al., Sleep, 2015). That is five 90-minute cycles or more. Children and teenagers need more.
Fifteen minutes is about the time it takes to fall asleep once you are in bed, typically around 10 to 20 minutes for a healthy adult. The cycles are counted from when you are asleep, not from when you lie down. Change the figure if you usually take longer.
Waking then may help, because sleep is lighter at the end of a cycle, but clock times cannot know where your cycles actually fall on a given night. Getting enough total sleep, at regular times, matters more than hitting a cycle boundary.
Formula only: no rates or limits are read from an official source.
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