Sleep cycle calculator
Health & fitnessHow can you plan your sleep?
Find bedtimes or wake times using an approximate 90-minute cycle.
What you enter stays on your device while you use this tool. Opening a shared link sends the settings in its address to HowToolbox to prepare the page.
24-hour time (HH:MM)
Sleep options · 5–6 cycles recommended
- 6 cycles · 9 h asleep
- 9:45 PM previous day
- 5 cycles · 7.5 h asleep
- 11:15 PM previous day
- 4 cycles · 6 h asleep
- 12:45 AM same day
- 3 cycles · 4.5 h asleep
- 2:15 AM same day
Suggested bedtime
9:45 PM
6 cycles · 9 hours of sleep · previous day
Sleep cycles vary. Shorter options may not provide enough sleep.
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Find bedtimes or wake times using an approximate 90-minute cycle.
How to use
- Choose whether you want bedtimes or wake times.
- Enter a clock time, or select Go to bed now. Adjust the minutes to fall asleep if needed.
- Compare the four options; five and six cycles are highlighted.
How it works
This planner treats a sleep cycle as 90 minutes. NHLBI describes cycles of about 80–100 minutes, so 90 is a convenient assumption, not a prediction of your sleep stages.
Bedtime = wake time − (cycles × 90 minutes) − time to fall asleep. To find a wake time, add those durations instead. For a 07:00 wake time, six cycles and 15 minutes to fall asleep give a bedtime of 21:45 the previous day.
Five to six cycles allow 7½–9 hours of sleep. The shorter options are comparisons, not a recommendation to restrict sleep. Clock changes are not accounted for. Prioritize sufficient sleep over hitting an exact cycle boundary.
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Frequently asked questions
Will I wake up refreshed at these times?
There is no guarantee. Cycles vary between people and through the night; this is a planning aid, not medical advice.
Is 15 minutes a measured average?
No. It is an editable starting assumption. Enter the time that is useful for your planning.
Does the time to fall asleep count as sleep?
No. It is added separately to the time in bed. Five modeled cycles are 450 minutes of sleep, plus your chosen time to fall asleep.
Does the planner adjust for daylight-saving time?
No. It adds or subtracts clock minutes and wraps at midnight. Check clock changes yourself on the night concerned.
Does the planner detect my sleep stages?
No. It uses the same 90-minute assumption for every cycle and does not measure your sleep.
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