Find optimal wake-up or bedtimes based on 90-minute sleep cycles to avoid grogginess.
Sleep Calculator
Health
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Select whether to find a wake time or bedtime.
Enter your target time.
Click Calculate for optimal times aligned to sleep cycles.
Sleep occurs in 90-minute cycles. Waking mid-cycle causes grogginess. Waking at cycle end feels refreshed. Calculator includes 15 min to fall asleep.
5–6 cycles (7.5–9 hours) is optimal for most adults.