Find bedtimes and alarm times that fit whole 90-minute sleep cycles.
Sleep runs in cycles of light, deep and dream (REM) sleep, each roughly 90 minutes long. Waking at the end of a cycle, when sleep is lighter, tends to feel easier than being pulled out of deep sleep halfway through. The calculator counts back (or forward) in 90-minute steps and adds 14 minutes, a typical time to fall asleep.
Ninety minutes is an average; real cycles vary from about 70 to 120 minutes between people and through the night. Treat the times as a good starting point and adjust if you still wake up groggy.
Health bodies recommend at least 7 hours a night for adults, which means 5 cycles (7.5 hours) or 6 (9 hours) on this calculator. Teenagers need more. Regular short nights add up, so use the 3 and 4 cycle options only now and then. This is general information, not medical advice; talk to a doctor about ongoing sleep problems.
For 7.5 hours of sleep (5 cycles), around 11:16 pm; for 9 hours (6 cycles), around 9:46 pm. Both include 14 minutes to fall asleep.
Most people take 10 to 20 minutes to fall asleep, so the bedtimes allow for that.
No. It's an average. If you wake up tired, try shifting your bedtime 10 to 15 minutes either way.
It can help plan a routine, but it isn't a treatment. See a doctor if sleep problems persist.
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