Sleep Cycle Calculator
Find the best time to go to bed or wake up based on sleep cycles, with your own fall-asleep time and cycle length and the recommended hours of sleep for your age.
How it works
bedtime = wake time − (cycles × cycle length) − time to fall asleep · wake time = bedtime + time to fall asleep + (cycles × cycle length)
Sleep runs in cycles of light sleep, deep sleep and REM that last about 90 minutes in adults. Waking at the end of a cycle tends to feel easier than waking in the middle of deep sleep, which causes the groggy alarm feeling. Choose whether you want to wake at a set time, go to bed at a set time or fall asleep now. The calculator then lists bedtimes or wake-up times for 3 or more full cycles, adding the time you need to fall asleep (15 minutes by default). Each option is checked against the recommended sleep for your age group from the CDC (based on the American Academy of Sleep Medicine and National Sleep Foundation guidance), and the starred one lands closest to the middle of that range. For most adults that means 5 cycles (7.5 hours) or 6 cycles (9 hours). If you know your cycles run shorter or longer, change the cycle length under More options.
Worked example
To wake at 6:30 AM with 5 cycles: 5 × 90 = 450 minutes of sleep, plus 15 minutes to fall asleep, is 465 minutes (7 h 45 min) in bed, so lights out at 10:45 PM. Six cycles (9 hours of sleep) means going to bed at 9:15 PM. If you go to bed at 11:00 PM instead, you fall asleep around 11:15 PM, and 5 cycles later the alarm should ring at 6:45 AM.
Sources: CDC — About sleep: how much sleep you need · American Academy of Sleep Medicine — recommended amount of sleep for pediatric populations (2016) · National Sleep Foundation — sleep duration recommendations
Frequently asked questions
Are cycles exactly 90 minutes?
No. They average 80–110 minutes and change through the night, with more deep sleep early and longer REM periods toward morning. Treat the times as approximate windows, not precise alarms. If you regularly wake just before the alarm, try a slightly shorter cycle length.
How much sleep do I need?
The CDC recommends 7 or more hours a night for adults aged 18–60, 7–9 hours at 61–64, and 7–8 hours from 65. Teens need 8–10 hours, school-age children 9–12, and preschoolers 10–13 including naps. Pick an age group and the calculator marks which options meet it.
Is 6 hours of sleep enough?
For nearly everyone, no. Adults need at least 7 hours. People who regularly sleep 6 hours perform worse in testing even when they report feeling fine.
What if I can’t fall asleep in 15 minutes?
Change the time to fall asleep to match your reality, and the times shift with it. A consistent wake time, dim evenings and a cool room usually shorten it. Regularly needing more than 30 minutes is worth discussing with a doctor.
What time should I go to bed to wake up at 7 AM?
With 15 minutes to fall asleep, go to bed at 11:15 PM for 5 cycles (7.5 hours of sleep) or at 9:45 PM for 6 cycles (9 hours).
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This is a general educational estimate, not medical advice. Bodies differ — for decisions about diet, training, medication or health conditions, talk to a doctor or registered dietitian.