Ever woken after a full night’s sleep still feeling groggy? Timing may be part of the reason. This calculator uses the natural rhythm of your sleep cycles to suggest bedtimes if you know when you need to wake, or wake-up times if you know when you are going to bed.
How the sleep calculator works
During the night, you move through repeating cycles of lighter sleep, deep sleep and REM (dream) sleep. A typical cycle lasts about 90 minutes, though it can range from about 80 to 110. Waking at the end of a cycle, when sleep is lightest, usually feels easier than being woken during deep sleep. The calculator counts back or forward in 90-minute blocks and adds about 15 minutes for the time it takes to fall asleep.
| Sleep cycles | Hours of sleep | Good for |
|---|---|---|
| 6 cycles | 9 hours | Teenagers, recovery, hard training |
| 5 cycles | 7.5 hours | Most adults |
| 4 cycles | 6 hours | Occasional short nights |
| 3 cycles | 4.5 hours | Emergencies only |
How much sleep do you need?
Most adults need seven or more hours a night, which is five or six full cycles. Teenagers need eight to ten hours, and school-age children nine to twelve. Cutting sleep short often catches up with you in mood, focus and health.
Tips to go with your new schedule
- Keep your bedtime and wake-up time consistent, even at weekends.
- Get morning daylight and dim the lights an hour before bed.
- Limit caffeine after early afternoon and avoid heavy meals close to bedtime.
- If you cannot fall asleep within about 20 minutes, get up and do something calm.
- Read our full guide: How to sleep better: 8 evidence-based habits.
- If stress keeps you up, try the five-minute reset.
See a professional if…
- You regularly struggle to sleep for three months or more.
- You snore loudly, gasp or stop breathing during sleep.
- You feel very sleepy during the day, especially while driving.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, although it varies between people and across the night.
Is it better to wake up at the end of a sleep cycle?
Many people find it easier to wake at the end of a cycle, when sleep is lighter. The effect is modest, and total sleep time matters most.
What time should I go to bed if I wake up at 6 a.m.?
Enter 6:00 AM above. For five cycles you would typically aim to be asleep by about 10:30 p.m., which means getting into bed around 10:15 p.m.
Are naps helpful?
A short nap of 20 to 30 minutes, finished before mid-afternoon, can boost alertness without disturbing night-time sleep.
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This calculator provides general estimates for healthy adults and is for information only. It is not medical advice and does not replace a conversation with a qualified healthcare professional. Read our disclaimer and editorial policy.