Sleep calculator (when to sleep or wake up)
Find the best time to sleep or wake up, based on 90-minute sleep cycles.
Bedtimes (recommended: 9h)
21:45
5 cycles (7.5h)23:15
4 cycles (6h)00:45
Each cycle is ~90 min; waking between cycles feels better. Includes ~15 min to fall asleep.
How the calculation works
Sleep happens in cycles of about 90 minutes. Waking at the end of a cycle (not mid-cycle) reduces grogginess. We count multiples of 90 min from your target time, plus ~15 min to fall asleep.
Frequently asked questions
How many hours should I sleep?
Adults: 7 to 9 hours, i.e. about 5 to 6 full cycles.
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Updated on June 18, 2026 · by Rafael Rossi · Methodology & sources