Sleep Calculator — A full sleep cycle is about 90 minutes long, going through light sleep, deep sleep, and REM. Waking up in the middle of a deep-sleep phase is what causes the grogginess and disorientation known as "sleep inertia." Waking at the end of a cycle — when sleep is naturally lightest — is much easier.
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Suggestions are general information based on average sleep cycles, not medical advice. Individual sleep needs vary. Persistent sleep problems deserve a conversation with a healthcare professional.
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A full sleep cycle is about 90 minutes long, going through light sleep, deep sleep, and REM. Waking up in the middle of a deep-sleep phase is what causes the grogginess and disorientation known as "sleep inertia." Waking at the end of a cycle — when sleep is naturally lightest — is much easier.
Most adults need 5 full cycles (about 7.5 hours of sleep) per night. Some do fine on 4 cycles (6 hours), and a few people genuinely need 6 cycles (9 hours). The tool shows all four options so you can pick what works for your schedule.
使用方法
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Pick a mode
"I need to wake up at" if you have a fixed wake time, or "I'm going to bed at" if bedtime is fixed.
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Enter the time
24-hour format. The tool accepts HH:MM.
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Adjust fall-asleep time
Default 15 min. Most people take 10-20 min to fall asleep; if you know yours, set it.
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Pick a cycle count
5 cycles (7.5h) is the most common. Try 4 if you have an early morning or 6 if you need the sleep.
示例
Wake up at 7:00 AM
Bedtime mode. Assuming 15 min to fall asleep.
结果： Best bedtimes: 9:15 PM (7 cycles), 10:45 PM (6 cycles), 12:15 AM (5 cycles), 1:45 AM (4 cycles)
Going to bed at 11:00 PM
Wake-up mode. Assuming 15 min to fall asleep.
结果： Best wake-up times: 4:30 AM (7 cycles), 6:00 AM (6 cycles), 7:30 AM (5 cycles), 9:00 AM (4 cycles)
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Last reviewed: 2026-09-25