Sleep Cycle Calculator
Optimize your sleep timing by aligning with natural 90-minute sleep cycles. Waking up between cycles instead of during one helps you feel refreshed and energized instead of groggy. Enter your target time below to find the best times to sleep or wake up.
How are sleep cycles calculated?
Sleep occurs in cycles of approximately 90 minutes each. During each cycle, you progress through four stages: light sleep (N1), deeper sleep (N2), deep sleep (N3/slow-wave), and REM (rapid eye movement) sleep where most dreaming occurs.
Waking up at the end of a complete cycle — during the lighter N1 or N2 stages — leaves you feeling alert and rested. Waking up in the middle of deep sleep (N3) or REM causes sleep inertia: that heavy, groggy feeling.
1 cycle = ~90 minutes
This calculator works backward (or forward) from your desired wake-up (or bedtime), adding the time it takes you to fall asleep, then computing the clock times that align with completing 3, 4, 5, or 6 full cycles.
Recommended sleep for adults (ages 18–64):
7–9 hours per night, or roughly 5–6 full sleep cycles.
Fewer than 4 cycles on a regular basis is associated with increased
health risks including impaired cognition, weakened immunity, and
mood disturbances.