Sleep Calculator
Wake up refreshed by timing your sleep around complete 90-minute sleep cycles. Tell us when you need to wake up, and we'll suggest the best bedtimes — or vice versa.
Formula reviewed for accuracy. Our methodology & sources
Sleep Calculator
health calculator
How It Works
Sleep moves through roughly 90-minute cycles, and waking at the end of a cycle feels far more refreshing than being jolted awake mid-cycle. The calculator assumes about 15 minutes to fall asleep, then counts complete 90-minute cycles either backward from your wake time to suggest bedtimes, or forward from now to suggest wake times. It offers several options because the ideal night is usually five or six full cycles rather than a fixed number of hours.
Formula
Sleep cycles are ~90 minutes. We add 15 minutes to fall asleep, then count back/forward in 90-minute cycles.
Examples
Wake at 07:00
Best bedtime around 21:45 for 6 full cycles.
Frequently Asked Questions
How do sleep cycles work?
Sleep occurs in cycles of about 90 minutes, moving through light, deep, and REM stages. Waking at the end of a cycle (rather than mid-cycle) helps you feel more refreshed.
How many hours of sleep do I need?
Most adults need 7-9 hours, which is about 5-6 complete sleep cycles. The calculator targets these cycle counts to align your wake time with the end of a cycle.
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