Sleep Cycle Calculator
When to Wake Up
Find optimal wake times based on when you go to sleep
When to Go to Sleep
Find optimal bedtimes based on when you need to wake up
Formula
Sleep cycle = ~90 minutes | Wake time = Bedtime + Fall asleep time + (Cycles x 90 min) | Bedtime = Wake time - Fall asleep time - (Cycles x 90 min) | Recommended: 5-6 cycles (7.5-9 hours)
Frequently Asked Questions
What is a sleep cycle?
A sleep cycle consists of four stages: NREM Stage 1 (light sleep, 5-10 min), NREM Stage 2 (deeper sleep, 20 min), NREM Stage 3 (deep/slow-wave sleep, 20-40 min), and REM sleep (dreaming, 10-60 min). One full cycle averages about 90 minutes.
How many sleep cycles do I need?
Most adults need 5-6 complete cycles (7.5-9 hours of sleep) per night. The National Sleep Foundation recommends 7-9 hours for adults aged 18-64, and 7-8 hours for adults 65+. Teens need 8-10 hours.
Why do I feel groggy when I wake up?
Sleep inertia (grogginess) is worse when you wake during deep sleep (NREM Stage 3). By timing your alarm to the end of a 90-minute cycle, you are more likely to wake during lighter sleep, feeling more alert and refreshed.
How long does it take to fall asleep?
The average healthy adult takes about 10-20 minutes to fall asleep (sleep latency). If you consistently fall asleep in under 5 minutes, you may be sleep-deprived. If it takes over 30 minutes regularly, you may have insomnia. Consult a sleep specialist if concerned.