Find the best times to fall asleep based on your wake-up time and natural 90-minute sleep cycles.
Sleep occurs in cycles of roughly 90 minutes. Waking up at the end of a cycle, rather than in the middle of one, tends to feel more refreshing — this calculator counts back from your wake time in 90-minute increments, plus 15 minutes to fall asleep.
A full sleep cycle — including light sleep, deep sleep, and REM — takes roughly 90 minutes on average, though this varies somewhat by individual.
Most adults need 7-9 hours per night. Waking at the end of a complete cycle within that range tends to feel better than waking mid-cycle, even if total time is similar.