Sleep Calculator
Find optimal sleep and wake times by cycle.
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Ctrl+Enter
You should go to bed at one of these times:
Includes ~15 minutes to fall asleep
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Frequently Asked Questions
Why are sleep cycles 90 minutes? +
A full sleep cycle moves through light sleep, deep sleep, and REM sleep, taking about 90 minutes on average. Waking up between cycles (rather than in the middle of one) helps you feel more rested and alert.
How many sleep cycles do I need per night? +
Most adults need 5-6 complete cycles per night, which works out to 7.5-9 hours of sleep. Some people function well on 4 cycles (6 hours), but consistently getting fewer than 5 cycles is linked to health problems.
Why does the calculator add 15 minutes to fall asleep? +
The average person takes about 14 minutes to fall asleep. The calculator accounts for this so your sleep cycles start from when you actually fall asleep, not when you get into bed. If you fall asleep faster or slower, adjust accordingly.
What if I wake up in the middle of a cycle? +
Waking mid-cycle, especially during deep sleep, causes grogginess called sleep inertia. It can last 15-30 minutes. This is why timing your alarm to the end of a cycle makes a noticeable difference in how you feel.
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