Sleep Calculator: find your best bedtime or wake-up time
Sleep comes in roughly 90-minute cycles. Pick a time and see when to go to bed or set your alarm.
How it works
During the night you move through light sleep, deep sleep, and REM sleep in repeating cycles of about 90 minutes. Waking at the end of a cycle, when sleep is lighter, often feels easier than being pulled out of deep sleep.
Cycle length and the time it takes to fall asleep both vary between people and from night to night, so treat every result as an estimate.
The calculator counts backwards from your wake-up time (or forwards from your bedtime) in 90-minute steps and adds about 15 minutes to fall asleep.
Tips
- A steady schedule matters more than a perfect cycle count.
- Dim lights and screens for an hour before bed.
- If you regularly wake up unrefreshed after 7 to 9 hours, consider talking to a clinician.
Want everyday habits to try alongside this estimate? Read our practical guide to better sleep.
Frequently asked questions
How long is one sleep cycle?
About 90 minutes for most adults, though it varies from roughly 70 to 120 minutes between people and from night to night. This calculator uses 90 minutes as a practical average.
Why does the calculator add 15 minutes?
Most people take some time to fall asleep. We add 15 minutes as a typical value; change your bedtime if you usually fall asleep faster or slower.
How many cycles do I need?
Most adults do well with 5 to 6 cycles (7.5 to 9 hours). Four cycles (6 hours) is a short night, and three cycles (4.5 hours) should be an exception.
Is waking at the end of a cycle guaranteed to feel better?
No. Cycle timing is an estimate. Total sleep, consistency, light, and stress all matter, so treat the results as a starting point.
