In short: sleep runs in cycles of about 90 minutes. Waking near the end of a cycle usually feels easier than waking in deep sleep. Enter your wake-up time and the calculator counts back 4, 5 or 6 cycles, plus the minutes you need to fall asleep.
Whole cycles
6, 7.5 or 9 hours of sleep, ending at the edge of a cycle.
Both ways
From your wake-up time to a bedtime, or from your bedtime to an alarm.
Track it in the app
Note how you slept each morning and see it next to stress, symptoms and your watch data.
How to use it
- Choose I want to wake up at and set the time, or I am going to bed at.
- Adjust the minutes you usually need to fall asleep (most adults: 10–20).
- Pick one of the three times. The middle one, 5 cycles or 7.5 hours, is highlighted because most adults need at least 7 hours.
How much sleep do adults need?
At least 7 hours a night, according to the American Academy of Sleep Medicine and the US CDC. Teenagers need 8–10 hours and school-age children 9–12. The calculator helps with timing; it cannot make up for too little sleep.
Frequently asked questions
Is every sleep cycle exactly 90 minutes?
No. 90 minutes is an average. Cycles range from about 70 to 120 minutes and change through the night, with more deep sleep early and more REM sleep towards morning. Treat the times as a starting point and adjust by 10–15 minutes if you still wake up groggy.
Which bedtime should I choose?
For most adults the 7.5-hour option is a good default. Choose 9 hours if you are catching up on sleep or feel tired during the day.
Does it work for naps?
A short nap of 10–20 minutes avoids deep sleep. A full 90-minute nap covers one cycle. The calculator is built for night sleep.
Is anything stored?
No. The times are calculated in your browser and nothing is sent anywhere.
When should I talk to a doctor about sleep?
If you often feel unrested after enough hours, snore loudly, stop breathing or gasp at night, or have trouble falling or staying asleep for weeks, talk to a doctor. These can be signs of a sleep disorder that needs proper assessment.
What time should I go to bed to wake up at 7?
To wake at 07:00 after 7.5 hours of sleep, with 15 minutes to fall asleep, go to bed at about 23:15. For 9 hours, about 21:45; for 6 hours, about 00:45.
