Sleep Calculator
Find the best time to go to bed — or wake up — based on 90-minute sleep cycles, so you rise refreshed instead of groggy.
Go to bed at one of these times:
Times marked ideal land 5–6 full sleep cycles — the sweet spot for most adults. A ★ marks the best fit for the selected age.
How sleep cycles work
While you sleep, your brain moves through repeating cycles of light sleep, deep sleep, and REM. Each full cycle lasts about 90 minutes, and a typical night contains five to six of them.
The trick to waking up refreshed is timing your alarm for the end of a cycle rather than the middle. Wake up mid-cycle — especially during deep sleep — and you get hit with sleep inertia: that heavy, groggy feeling that can linger for an hour. Wake at the end of a cycle, when sleep is lightest, and getting up feels far easier.
This calculator counts whole 90-minute cycles back from your alarm (or forward from your bedtime) and adds about 14 minutes to fall asleep, then shows you the times that line up with the end of a cycle.
How much sleep do you need?
Cycle timing matters, but so does total sleep. Recommended amounts shift with age:
| Age group | Recommended sleep |
|---|---|
| Teen (13–17) | 8–10 hours |
| Adult (18–64) | 7–9 hours |
| Older adult (65+) | 7–8 hours |
Popular bedtimes & wake-up times
To wake up at…
Frequently asked questions
How does the sleep calculator work?
It counts backward from your wake-up time (or forward from your bedtime) in 90-minute sleep cycles, adding about 14 minutes to fall asleep. Waking at the end of a cycle rather than the middle helps you feel more refreshed.
How long is one sleep cycle?
A full sleep cycle lasts roughly 90 minutes, moving through light sleep, deep sleep, and REM. Cycle length varies a little between people and across the night, but 90 minutes is the standard estimate.
How many sleep cycles do I need?
Most adults do best with five to six complete cycles per night — about 7.5 to 9 hours of sleep. Teenagers generally need more, and needs shift slightly with age.
Why is it better to wake up at the end of a cycle?
If your alarm goes off during deep sleep, you wake up groggy and disoriented — a state called sleep inertia. Waking at the end of a cycle, when sleep is lightest, makes getting up feel easier.
How long should it take to fall asleep?
Falling asleep in 10 to 20 minutes is typical; the average is about 14 minutes, which this calculator assumes by default. You can adjust it if you tend to drift off faster or slower.
Sleep better tonight
The right mattress and bedding make good sleep timing pay off. Explore our tested guides: