Sleep Calculator
This sleep calculator suggests bedtimes or wake-up times that line up with complete 90-minute sleep cycles, including the time you usually take to fall asleep, so you are more likely to wake between cycles rather than in deep sleep.
About this tool
This sleep calculator suggests bedtimes or wake-up times that line up with complete 90-minute sleep cycles, including the time you usually take to fall asleep, so you are more likely to wake between cycles rather than in deep sleep.
How to use it
- Choose whether you want to wake up at a set time, go to bed at a set time, or go to sleep now.
- Enter the time (not needed for going to sleep now).
- Set how many minutes you usually take to fall asleep.
- Pick one of the suggested times; options with 5–6 cycles are highlighted as ideal.
Good to know
- The calculator assumes 90-minute sleep cycles.
- It suggests times for 3 to 6 complete cycles — 4.5 to 9 hours of sleep.
- The minutes you take to fall asleep are added before the first cycle starts.
- Five to six cycles (7.5–9 hours) fits the 7–9 hours of sleep most adults are recommended.
Runs entirely in your browser — nothing you enter is uploaded or stored.
Frequently asked questions
How long is a sleep cycle?
A sleep cycle averages about 90 minutes, although it varies between roughly 70 and 120 minutes across people and through the night.
Why do I feel groggy even after enough sleep?
Waking from deep sleep can cause sleep inertia, a groggy feeling that can last up to 30 minutes. Timing your alarm to the end of a cycle may help, although cycle lengths are not exact.
How many hours of sleep do adults need?
Most adults need 7–9 hours per night, which is about five to six 90-minute cycles.
How long does it take to fall asleep?
Healthy adults typically fall asleep within about 10–20 minutes. Taking far longer or falling asleep almost instantly every night can be a sign of a sleep problem or sleep debt.