How sleep cycle calculator works
Sleep happens in cycles of roughly 90 minutes. Waking at the end of a cycle (rather than in the middle of one) leaves you feeling refreshed, so this calculator plans your sleep in whole multiples of one cycle.
Choose 'Wake at' and enter the time you must wake up: the tool counts back in 3 to 6 cycles, adding a few minutes to fall asleep, and lists the bedtimes that will have you waking at the end of a cycle.
Choose 'Sleep now' and enter the time you are going to bed: it counts forward and lists the wake-up times you should aim for. Times of 5 to 6 cycles are highlighted as recommended for most adults, while 3 to 4 cycles still leave you rested on a tight schedule.
Frequently asked questions
Why 90-minute sleep cycles?
Most adults move through a full sleep cycle (light, deep, and REM sleep) in about 90 minutes. Waking at the end of a cycle tends to feel easier than being jolted out of deep sleep, so timing sleep in multiples of 90 minutes helps you wake up refreshed.
How many sleep cycles do I need?
Most adults do best with 5 to 6 full cycles (about 7.5 to 9 hours), which is why those options are highlighted as recommended. 3 to 4 cycles (4.5 to 6 hours) can work for a short night or a nap but is not ideal long-term.
Why is there a delay before the sleep time?
The calculator adds a few minutes (15 by default) for the time it takes to fall asleep before the first cycle starts. You can adjust this and the cycle length to match your own body.
Do these times work for shift work or naps?
Yes. The tool works with any 24-hour clock time and wraps past midnight automatically, so it works for night shifts, early starts, or planning a nap. Just enter the wake or sleep time that fits your schedule.
