Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles.
Sleep Cycle Calculator
Recommended Times (in 90-minute cycles)
Why Sleep Cycles Matter
Sleep happens in cycles of roughly 90 minutes, moving through light sleep, deep sleep, and REM sleep. Waking up in the middle of a cycle, especially during deep sleep, tends to leave you feeling groggy, while waking up at the end of a complete cycle feels more natural and refreshed.
This calculator adds a 15-minute buffer to fall asleep, then works in 90-minute increments to suggest bedtimes or wake-up times that align with complete sleep cycles.
Frequently Asked Questions
Why 90-minute cycles specifically?
90 minutes is the commonly cited average length of a full sleep cycle, though individual cycle length can vary somewhat from person to person.
Why does it add 15 minutes before the first cycle?
This accounts for the typical time it takes to actually fall asleep after getting into bed, so the cycles align with real sleep time, not just time in bed.
How many cycles should I aim for?
Most adults benefit from 5-6 complete cycles per night (7.5-9 hours), though individual sleep needs vary.