Sleep cycle calculator
Tell me when your alarm goes off (or when you're heading to bed) and I'll suggest the best times to wake up at the end of a sleep cycle — not in the middle of one.
The calculation includes about 15 minutes to fall asleep.
Why count 90-minute sleep cycles
Sleep isn't uniform through the night: it moves in cycles of roughly 90 minutes, shifting from light sleep into deep sleep and then REM. If your alarm goes off in the middle of deep sleep, you feel groggy even after plenty of rest — that foggy feeling is called "sleep inertia". Waking up at the end of a cycle, when sleep is light again, makes getting up much easier. That's why this calculator suggests times in multiples of 90 minutes, adding about a quarter of an hour for the average time it takes to fall asleep.
How many sleep cycles do you need?
For most adults the sweet spot is 5 or 6 cycles — between 7.5 and 9 hours of sleep — and those are the times highlighted in green in the results. Four cycles (6 hours) can work occasionally, while three cycles (4.5 hours) should be treated as an emergency, not a habit. Keep in mind that cycle length varies from person to person, roughly between 80 and 110 minutes. This tool provides estimates only and is not medical advice — see a doctor if you have persistent sleep problems.