Sleep Cycle Calculator
Find the best times to go to sleep or wake up based on 90-minute sleep cycles. Enter a wake time for bedtimes, or a bedtime for wake times.
Calculator by Toolsloft ↗- 6 cycles (9.0 h sleep)
- Go to sleep at 21:45
- 5 cycles (7.5 h sleep)
- Go to sleep at 23:15
- 4 cycles (6.0 h sleep)
- Go to sleep at 00:45
- 3 cycles (4.5 h sleep)
- Go to sleep at 02:15
Waking at the end of a sleep cycle, rather than in the middle of one, tends to leave you feeling more rested. This calculator works in 90-minute cycles: tell it when you need to wake up and it lists bedtimes, or tell it when you are going to bed and it lists good wake-up times.
How this is calculated
Sleep is modeled as repeating 90-minute cycles, the commonly cited average cycle length, plus 15 minutes to fall asleep. From a wake time we subtract 15 minutes plus 6, 5, 4, or 3 full cycles to get candidate bedtimes; from a bedtime we add the same offsets to get candidate wake times. Real cycles vary from person to person and night to night, so treat these as guides.
How to use
- Choose whether you know your wake-up time or your bedtime.
- Enter that time in 24-hour HH:MM format.
- Read the suggested times, ordered from the longest sleep (6 cycles) to the shortest (3 cycles).
Examples
- Need to wake at 07:00:
Fall asleep by 21:45, 23:15, 00:45, or 02:15 - Going to bed at 23:00:
Wake at 08:15, 06:45, 05:15, or 03:45
FAQ
- How long is one sleep cycle?
- About 90 minutes on average, moving through light sleep, deep sleep, and REM. This tool uses 90 minutes as the cycle length.
- Why add 15 minutes?
- Most people take around 15 minutes to fall asleep after getting into bed, so the calculator adds that buffer before counting cycles.
- Which option should I pick?
- Adults generally do best with 5 to 6 cycles (about 7.5 to 9 hours). The shorter 3 and 4 cycle options are there for nights when a full sleep is not possible.