Find the best time to go to bed or wake up, based on 90-minute sleep cycles.
Sleep happens in cycles that last about 90 minutes each, moving through light sleep, deep sleep, and REM. Waking up at the end of a cycle — rather than in the middle of one — generally feels easier and leaves you less groggy.
This calculator adds a 15-minute buffer to fall asleep, then counts in 90-minute blocks to suggest times that line up with the end of a full cycle. Most adults do best with 5–6 cycles (7.5–9 hours) of sleep a night.