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Sleep Calculator

Find optimal bedtimes and wake times based on 90-minute sleep cycles. Wake up refreshed, not groggy.

Recommended bedtimes (includes ~15 min to fall asleep):

Recommended wake-up times (includes ~15 min to fall asleep):

Uses your current time. Recommended wake-up times:

About Sleep Cycles

Sleep cycles last approximately 90 minutes and include stages of light sleep, deep sleep, and REM (rapid eye movement) sleep. Most adults need 5 to 6 complete cycles per night, which translates to 7.5 to 9 hours of sleep. Waking up at the end of a cycle — rather than in the middle of one — helps you feel alert and refreshed instead of groggy. This calculator factors in about 15 minutes to fall asleep, then counts backward or forward in 90-minute intervals to find your ideal bedtime or wake-up time.

FAQ

What is a sleep cycle?
A sleep cycle is a roughly 90-minute period during which your body progresses through several stages: light sleep (N1 and N2), deep sleep (N3), and REM sleep. You typically go through 4 to 6 cycles per night. Each cycle's composition changes throughout the night — earlier cycles have more deep sleep, while later cycles have more REM sleep.
How much sleep do I need?
Most adults need 7 to 9 hours of sleep per night, which corresponds to 5 or 6 complete 90-minute cycles. Teenagers need about 8 to 10 hours, school-age children need 9 to 12 hours, and younger children and infants need even more. Consistently sleeping less than 7 hours is associated with increased health risks.
Why 90-minute cycles?
Research has shown that the average sleep cycle lasts about 90 minutes, though it can range from 80 to 120 minutes depending on the individual. Waking at the end of a cycle (during light sleep) rather than in the middle (during deep sleep) reduces sleep inertia — that groggy, disoriented feeling. The 90-minute figure is a reliable average for most people.
What if I take longer to fall asleep?
This calculator assumes an average of 15 minutes to fall asleep. If you typically take longer, adjust your bedtime earlier accordingly. For example, if you usually take 30 minutes to fall asleep, go to bed 15 minutes earlier than the times shown. Practicing good sleep hygiene — avoiding screens, keeping a cool room, and maintaining a consistent schedule — can help you fall asleep faster.

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