Sleep Cycle Calculator
Find the best times to fall asleep or wake up based on 90-minute sleep cycles.
How it works
bedtime = wake time − (cycles × 90 min) − 15 min to fall asleep
Sleep runs in roughly 90-minute cycles from light to deep to REM. Waking at a cycle boundary tends to feel easier than waking mid-deep-sleep, which is the groggy alarm feeling. Five to six full cycles (7.5–9 h) suits most adults.
Worked example
To wake at 6:30 AM after 6 cycles: 6 × 90 = 540 minutes plus 15 to fall asleep — lights out at 9:15 PM.
Frequently asked questions
Are cycles exactly 90 minutes?
They average 80–110 minutes and lengthen through the night, so treat the boundaries as approximate windows, not precise alarms.
Is 6 hours of sleep enough?
For nearly everyone, no — adult guidance is 7–9 hours. Chronic 6-hour sleepers underperform in testing while reporting they feel fine.
What if I can’t fall asleep in 15 minutes?
Adjust the buffer to your reality. Consistent wake time, dim evenings and a cool room shorten it over time.
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This is a general educational estimate, not medical advice. Bodies differ — for decisions about diet, training, medication or health conditions, talk to a doctor or registered dietitian.