Sleep Calculator — When to Go to Bed or Wake Up
Wake up between sleep cycles instead of in the middle of one. Enter when you need to get up or when you are going to bed, and get times that line up with roughly 90-minute cycles.
Go to bed at one of these times
How to use the sleep calculator
- Choose whether you know your wake-up time or your bedtime (or are heading to bed right now).
- Enter the time and how long it usually takes you to fall asleep. The average is about 15 minutes.
- Pick one of the suggested times. The highlighted options give 5–6 full cycles, which is 7½ to 9 hours of sleep.
How sleep cycles work
Sleep moves through repeating cycles of light sleep, deep sleep and REM (dreaming) sleep, each lasting roughly 90 minutes on average. Waking at the end of a cycle, when sleep is lightest, tends to feel easier than being jolted out of deep sleep, which can leave you groggy for a while (sleep inertia).
This calculator counts back or forward in 90-minute cycles and adds the time it takes to fall asleep. Cycle length varies from person to person and through the night (anywhere from about 70 to 120 minutes), so treat the times as a starting point and adjust by 15 minutes if you still wake up groggy.
Total sleep matters more than precise timing. The American Academy of Sleep Medicine recommends at least 7 hours a night for adults, teens need 8–10, and school-age children 9–12. A consistent schedule, even on weekends, is one of the most effective ways to sleep better.
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Frequently asked questions
How many sleep cycles do I need?
Most adults need 5 or 6 cycles, about 7½ to 9 hours.
Is a sleep cycle always 90 minutes?
No. 90 minutes is an average; cycles range from about 70 to 120 minutes and change through the night.
What if I wake up during the night?
That is normal. Brief awakenings between cycles are common and usually forgotten.
Is this medical advice?
No. If you regularly feel unrested, snore loudly or have trouble sleeping, talk to a doctor.