Sleep Cycle Calculator
I want to
10–20 minutes is typical
Averages about 90; ranges 70–120
Go to bed at one of these times to wake at 7:00 AM
- 9:45 PM21:456 cycles · 9 h of sleep · ideal
- 11:15 PM23:155 cycles · 7 h 30 min of sleep · good
- 12:45 AM00:454 cycles · 6 h of sleep · short
- 2:15 AM02:153 cycles · 4 h 30 min of sleep · too short for regular nights
Each time already includes 15 minutes to fall asleep. Waking at the end of a cycle, in light sleep, tends to feel easier than waking from deep sleep. Adults need at least 7 hours a night, so five or six cycles is the target; cycle length varies between people and through the night, so treat the times as a guide.
Find bedtimes that let you wake up at the end of a sleep cycle, or the best wake-up times for when you go to bed, counting cycles of about 90 minutes plus the time it takes you to fall asleep.
Formula
Worked Example
Five 90-minute cycles back from 7:00 AM is 11:30 PM, and allowing 15 minutes to fall asleep makes the bedtime 11:15 PM. Five or six cycles meets the adult minimum of 7 hours.
Frequently Asked Questions
How long is a sleep cycle?
About 90 minutes on average, but it varies from roughly 70 to 120 minutes between people and through the night: early cycles hold more deep sleep and later ones more REM sleep. Treat the times as a guide, and lengthen or shorten the cycle if you often wake up groggy.
How much sleep do adults need?
At least 7 hours a night, according to the American Academy of Sleep Medicine and the Sleep Research Society. Teenagers need 8–10 hours and children aged 6–12 need 9–12.
Why do I sometimes feel worse after more sleep?
Waking from deep sleep brings on sleep inertia, a groggy spell that often lasts 15–30 minutes. Waking near the end of a cycle, when sleep is lighter, usually feels easier, which is why 7½ hours can feel better than 8.