Sleep Cycle Calculator — Best Bedtimes to Wake Up Refreshed
Calculate optimal bedtimes based on 90-minute sleep cycles. Enter wake-up time or bedtime and get timing that avoids deep sleep interruptions.
Mode
💤 Go to sleep at…
12:46 AM
4 cycles (6h)
⭐ Recommended
11:16 PM
5 cycles (7.5h)
09:46 PM
6 cycles (9h)
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Frequently Asked Questions
Quick answers to common questions
How long is one sleep cycle?+
One complete sleep cycle is approximately 90 minutes and includes N1 light sleep (5-10 min), N2 deeper sleep (20-25 min), N3 deep slow-wave sleep (20-40 min), and REM sleep (10-20 min). Most adults need 4-6 complete cycles (6-9 hours total).
Why do I feel groggy after 8 hours of sleep?+
Grogginess occurs when you wake during deep sleep (N3) rather than at a cycle's end. Calculate cycles and set alarms at 90-minute intervals from when you expect to fall asleep. This tool adds a 14-minute sleep onset delay automatically.
How many hours of sleep does an adult need?+
Adults need 7-9 hours per night — that is 5-6 complete 90-minute cycles. Consistently sleeping under 6 hours is associated with increased cardiovascular and cognitive risks.