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Sleep Cycle Calculator
Find the best bedtime or wake-up time, based on completing full 90-minute sleep cycles.
Suggested wake times are calculated from your device's current time.
This tool is a general estimate based on average sleep cycle length and is not a substitute for professional medical advice; talk to a doctor if you have ongoing sleep problems.
How do sleep cycles work?
A night's sleep is made up of several back-to-back cycles, each lasting about 90 minutes on average and including light sleep, deep sleep and REM (dream) sleep. Waking up in the middle of a cycle — especially during deep sleep — tends to leave you groggy, a feeling known as "sleep inertia," while waking near the end of a full cycle usually feels more refreshing, even with fewer total hours of sleep.
This calculator assumes 15 minutes to fall asleep and works out optimal sleep or wake times for 3, 4, 5 and 6 complete cycles. If you have a fixed wake-up time, it counts backward to show good bedtimes; if you're about to sleep right now, it counts forward to show good wake-up times. For most adults, completing 5 to 6 cycles (7.5 to 9 hours) is the ideal target.
Frequently asked questions
What is a 90-minute sleep cycle?
Human sleep is made up of repeating cycles, each averaging about 90 minutes and including light, deep and REM sleep stages.
Why does the calculator add 15 minutes?
Most people don't fall asleep the instant they lie down; 15 minutes is a common average for sleep onset, which this tool factors into its calculations.
Why is waking up mid-cycle worse than at the end of one?
Waking during deep sleep tends to cause grogginess ("sleep inertia"), while waking near the end of a completed cycle, when sleep is lighter, usually feels more refreshing.
How many cycles should I aim for?
Most adults feel best after 5 to 6 complete cycles, or about 7.5 to 9 hours of sleep, though individual needs vary.