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90-minute sleep cycles

Sleep Calculator

Bedtime & wake-up by sleep cycle

In short

Sleep runs in roughly 90-minute cycles, so waking between cycles feels easier. Tell this calculator when you want to wake up, or when you are going to bed, and it steps in 90-minute intervals to suggest bedtimes or wake-up times for five to six full cycles, plus time to fall asleep.

Sleep Cycles

Wake up between cycles

Sleep by full cycles, wake up refreshed

Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle — rather than in the middle of one — tends to feel easier and less groggy. This sleep calculator works backwards or forwards in 90-minute steps so you can aim to wake between cycles.

Tell it when you need to wake up and it suggests bedtimes for 6, 5 and 4 completed cycles (about 9, 7.5 and 6 hours). Tell it when you're going to bed — or choose “now” — and it suggests wake-up times for the same cycle counts. A short buffer of about 15 minutes to fall asleep is built in.

General guide: Most adults do best on 7–9 hours (about 5–6 cycles). This tool is a planning aid, not medical advice — if you often sleep poorly, it's worth speaking to a doctor.

Why 90-minute cycles

Across a night you move through light sleep, deep sleep and REM in a repeating cycle that averages around 90 minutes. Cycle length varies from person to person and night to night, so treat the suggested times as close targets rather than exact science, and adjust to what leaves you feeling rested.

Related tools

To measure hours between two times, use the hours & duration calculator; to add or subtract time, the time calculator.

FAQ

Common questions

How does the sleep calculator work?
It counts in 90-minute sleep cycles. Enter when you want to wake up and it suggests bedtimes for 6, 5 and 4 cycles; enter a bedtime and it suggests wake-up times, with about 15 minutes added to fall asleep.
How many hours of sleep should I get?
Most adults do best on 7 to 9 hours — roughly 5 to 6 full cycles. Needs vary by person and age, so use how you feel as the real guide.
Why 90-minute cycles?
A full sleep cycle through light, deep and REM sleep averages about 90 minutes. Waking between cycles rather than mid-cycle tends to feel less groggy.
Is this medical advice?
No. It's a planning aid based on average cycle length. If you regularly struggle with sleep or feel unrested, consider speaking with a doctor.
Sources & standards
  • Method: bedtimes and wake times aligned to roughly 90-minute sleep cycles, plus about 15 minutes to fall asleep.
  • Guidance: most adults need 7–9 hours (about 5–6 cycles) — National Sleep Foundation.
  • Note: a general planning aid, not medical advice.
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