Wake at 07:00, 15 minutes to fall asleep
Go to bed at 23:15 for five cycles, or 21:45 for six.
Sleep calculator
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A sleep cycle is taken as 90 minutes and falling asleep as the minutes you enter. Real cycles vary from about 70 to 120 minutes between people and through the night, so treat the times as a guide. Most adults need 7 to 9 hours.
I want to
Go to bed at
23:15
11:15 PM gives five full 90-minute cycles, 7 h 30 min of sleep, plus 15 minutes to drift off. For nine hours, aim for 9:45 PM.
- Five cycles
- 11:15 PM
- Six cycles
- 9:45 PM
- Time asleep, 5 cycles
- 7 h 30 min
Bedtimes to wake at 7:00 AM
| Cycles | Sleep | 24-hour | 12-hour | Verdict |
|---|---|---|---|---|
| 6 cycles | 9 h 00 min | 21:45 | 9:45 PM | Recommended |
| 5 cycles | 7 h 30 min | 23:15 | 11:15 PM | Recommended |
| 4 cycles | 6 h 00 min | 00:45 | 12:45 AM | Short night |
| 3 cycles | 4 h 30 min | 02:15 | 2:15 AM | Nap-like |
Timing sleep around cycles
Sleep runs in cycles of light sleep, deep sleep and REM, each lasting about 90 minutes. Waking at the end of a cycle, when sleep is light, usually feels easier than being pulled out of deep sleep by an alarm. That is the idea behind this calculator.
Say you need to be up at 07:00 and usually fall asleep in 15 minutes. Five cycles take 7 hours 30 minutes, so lights out should be 23:15. Six cycles, a full 9 hours, means 21:45. Four cycles, at 00:45, gives only 6 hours and is best kept for an emergency.
Going the other way works the same. If you get into bed at 23:00, you are likely asleep by 23:15 and at the end of a fifth cycle at 06:45. If you can sleep in, 08:15 completes a sixth.
Treat the times as a starting point. Cycle lengths differ between people and get shorter toward morning. The surest signs you are getting enough are waking without an alarm on most days and not feeling sleepy in the afternoon. If you snore loudly or still feel tired after 8 hours, speak to a doctor.
Sources
What this calculator does not account for
- Your own cycle length, which can be 70 to 120 minutes.
- Sleep disorders, shift work and jet lag.
- Night waking and naps.
How this is calculated
Formula: Sleep cycle timing
bedtime =wake time − time to fall asleep − cycles × 90 minWhat the symbols mean
- cyclesFull sleep cycles. Five is 7 h 30 min and six is 9 hours.
- time to fall asleepMost people take 10 to 20 minutes.
Good to know
- In bedtime mode the sums run the other way: wake time = bedtime + time to fall asleep + cycles × 90 min.
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Worked examples
Each example is worked out by the same code as the calculator above.
Bed at 23:00
Wake at 06:45 after five cycles.
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<iframe src="/embed/sleep-calculator" title="Sleep calculator" width="100%" height="720" style="border:0;max-width:42rem" loading="lazy"></iframe>Questions
What time should I go to bed to wake up at 7 am?
Around 11:15 pm for five 90-minute cycles, or 9:45 pm for six, if you take about 15 minutes to fall asleep.
If I go to bed at 11 pm, when should I wake up?
About 6:45 am after five cycles, or 8:15 am after six, allowing 15 minutes to fall asleep.
How long is a sleep cycle?
About 90 minutes on average, though it ranges from roughly 70 to 120 minutes and changes through the night.
How many hours of sleep do adults need?
The CDC and the American Academy of Sleep Medicine recommend 7 or more hours a night for adults. Teenagers need 8 to 10.
Why do I feel groggy after a long sleep?
Waking from deep sleep causes sleep inertia, that heavy, slow feeling. Ending near the close of a cycle tends to feel easier.