Sleep Cycle Calculator
Work out the best bedtime so you wake at your chosen time after a whole number of 90 minute sleep cycles.
Recent
Formula
How the calculation works
The calculator starts from your wake time and subtracts one 90 minute cycle for every cycle you want to complete.
It then subtracts the number of minutes you usually need to fall asleep, which is the 15 minute buffer in the default.
The result is the exact clock time you should be in bed so the alarm falls at the end of a cycle.
Common mistakes
- Forgetting the fall asleep buffer and getting into bed at the calculated time instead of 15 minutes before it.
- Choosing six cycles every night, which can leave too little time for a full night and build up a sleep debt.
When to use it
- People who wake at a fixed time use it to set a bedtime that lands between sleep cycles instead of in the middle of deep sleep.
- Students and shift workers use it to plan a nap or a full night and still feel alert when the alarm goes off.
Worked example
Waking at 06:00 after 5 cycles with 15 minutes to fall asleep means going to bed at 22:15.
Common questions
Why 90 minutes for one cycle?
A full sleep cycle of light, deep and REM sleep lasts about 90 minutes on average, though it ranges from 80 to 120 minutes for different people.
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