Sleep Cycle Calculator
Wake up refreshed. Calculate ideal bedtimes or wake-up times aligned with your natural 90-minute sleep cycles.
Best times to go to sleep:
Why sleep cycles matter
Sleep isn't one long state — it's a series of repeating cycles, each lasting about 90 minutes. Each cycle includes four stages: N1 (light sleep), N2 (consolidated sleep), N3 (deep/slow-wave sleep), and REM (rapid eye movement sleep, associated with dreaming and memory consolidation).
Why you feel groggy in the morning
If your alarm goes off during deep sleep (N3), you experience sleep inertia — that foggy, disoriented feeling that can last 30–60 minutes. Waking at the end of a sleep cycle, when you're in lighter sleep, dramatically reduces this effect.
How many cycles do you need?
Most adults need 5–6 complete cycles per night (7.5–9 hours). Teenagers and older adults have slightly different needs. Quality matters as much as quantity — consistent sleep and wake times, a dark room, and limiting screens before bed all improve cycle quality.