Sleep Calculator
Free to use. Runs in your browser: your files and text are not uploaded.
This tool gives general information only. It is not medical advice.
Choose when you need to wake up, or when you are going to bed, and see times that fit whole sleep cycles.
How to use it
- Choose whether you know your wake-up time or your bedtime.
- Set the time.
- Read the suggested times for 6, 5, 4 and 3 sleep cycles.
How it works
Sleep moves through stages in a repeating cycle: light sleep, deep sleep, and REM sleep, when most dreaming happens. One cycle lasts about 90 minutes in adults. People often feel groggier when an alarm wakes them from deep sleep than from light sleep, so the idea is to time the alarm for the end of a cycle.
The tool counts back or forward in 90-minute blocks and adds 15 minutes, a typical time to fall asleep.
Example: to wake at 7:00 AM after five cycles: 5 × 90 minutes = 7 hours 30 minutes of sleep, plus 15 minutes to fall asleep. Bedtime is 7 hours 45 minutes before 7:00 AM, which is 11:15 PM.
| Cycles | Sleep | Bedtime for a 7:00 AM alarm |
|---|---|---|
| 6 | 9 hours | 9:45 PM |
| 5 | 7.5 hours | 11:15 PM |
| 4 | 6 hours | 12:45 AM |
| 3 | 4.5 hours | 2:15 AM |
Five or six cycles meet the 7-hour recommendation for adults. Three and four are shown for nights when a short sleep cannot be avoided.
Limits
- 90 minutes is an average. Your cycles may be shorter or longer, and they change through the night, so the times are a guide, not a guarantee.
- If you usually take more or less than 15 minutes to fall asleep, shift the times to match.
- Getting enough total sleep, at regular times, matters more than hitting the end of a cycle.
- Ongoing trouble sleeping, loud snoring or daytime sleepiness are reasons to see a doctor.
Frequently asked questions
What time should I go to bed to wake up at 7 AM?
For five full sleep cycles, go to bed at 11:15 PM. For six cycles, 9:45 PM. Both allow 15 minutes to fall asleep.
How long is a sleep cycle?
About 90 minutes on average in adults, but it varies from roughly 70 to 120 minutes between people and through the night.
How many hours of sleep do adults need?
Sleep medicine bodies in the United States recommend 7 or more hours a night for adults. Teenagers and children need more.