Calculate the best time to wake up or go to sleep based on 90-minute sleep cycles for feeling refreshed.
This calculator uses two common rules of thumb: a sleep cycle of roughly 90 minutes and about 15 minutes to fall asleep. Real cycle length and falling-asleep time vary between people and from night to night, so treat the times as a guide, not exact predictions. CDC lists 7 or more hours of sleep for adults aged 18 to 60 (CDC), which is 5 or more cycles here. Aim for a steady schedule.
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