The Best Time To Sleep Calculator
The clock decides how you feel in the morning as much as the hours do. Counting backwards in 90 minute cycles from your alarm finds the bedtimes that land between cycles instead of inside one.
Recommended bedtime
23:15
- 6 cycles (9 h sleep)
- 21:45 (previous day)
- 5 cycles (7.5 h sleep)
- 23:15 (previous day)
- 4 cycles (6 h sleep)
- 00:45
Five cycles is the usual target. Each step is a full 90 minutes, so the choice between four, five and six cycles is a real decision rather than a rounding error.
The formula this calculator uses
bedtime = wake time - (15 + 90 x cycles)
- cycles
- Number of 90 minute sleep cycles, usually four to six
- fallAsleep
- Minutes taken to drop off, commonly about 15
- wake time
- The time your alarm is set for
- bedtime
- The time to get into bed so the cycle ends with the alarm
How to check the result by hand
- 1
Fix the wake time first
Everything counts back from the alarm. If you want to wake at 07:00, that is the anchor, and the bedtime is whatever the arithmetic produces.
- 2
Add fifteen minutes to fall asleep
Getting into bed is not the same as sleeping. Most people take around a quarter of an hour to drop off, so the in-bed time has to start earlier than the sleep time.
- 3
Subtract whole 90 minute cycles
Six cycles is 540 minutes, five is 450, four is 360. Use whole cycles only, because a half cycle lands the alarm in the middle of deep sleep.
- 4
Combine the two and wrap past midnight
For a 07:00 alarm, six cycles plus the fifteen minutes is 555 minutes earlier, which is 21:45. Five cycles gives 23:15 and four gives 00:45 the same night.
- 5
Pick the option that fits your evening
Choose the cycle count that gets you into bed at a realistic hour, and treat the neighbouring options as a clear ninety minute step rather than a few minutes of negotiation.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate The Best Time To Sleep page.