Find the best bedtime or wake-up time based on 90-minute sleep cycles. Waking at the end of a cycle means you feel more refreshed — even with fewer hours of sleep.
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Know what time you need to wake up? Use "wake up at". Prefer to set bedtime? Use the other option.
Enter your wake-up or bedtime using the time picker.
Pick the bedtime that gives you the most complete cycles before your wake-up. 5 cycles (7.5h) is ideal for most adults.
Sleep occurs in 90-minute cycles. Each cycle includes light sleep, deep sleep, and REM. Waking mid-cycle (during deep sleep) causes grogginess.
Most adults need 5–6 full cycles (7.5–9 hours). The calculator shows 4 options so you can choose based on when you actually need to sleep.
A sleep cycle lasts approximately 90 minutes and includes stages: light sleep (N1, N2), deep sleep (N3), and REM sleep. One full night typically has 4–6 complete cycles.
8 hours may not align with complete 90-minute cycles — you might be waking mid-cycle. 7.5 hours = 5 complete cycles, which often feels better than 8 hours of interrupted cycles.
The average is 10–20 minutes. Less than 5 minutes suggests sleep deprivation. More than 30 minutes may indicate insomnia. Use 15 minutes as the default.
Most adults need 7–9 hours (5–6 cycles). Teenagers need 8–10 hours. Children under 12 need 9–11 hours. Quality matters as much as quantity.
Adults need 7-9 hours per night. Teenagers need 8-10 hours. Children aged 6-12 need 9-12 hours. Sleep deprivation accumulates as a debt — one hour less each night for a week creates a 7-hour deficit.