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Sleep Calculator
Find the best time to go to bed or wake up so you finish full 90-minute sleep cycles and wake up feeling rested.
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How to use this calculator
Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
How sleep cycles work
Each night you move through cycles of light sleep, deep sleep and REM that last about 90 minutes on average (70–120 minutes). Waking at the end of a cycle, when sleep is light, usually feels easier than being woken from deep sleep.
bedtime = wake-up time − cycles × 90 min − time to fall asleep
Example: to wake at 7:00 AM with 15 minutes to fall asleep, go to bed at 9:45 PM (6 cycles, 9 h) or 11:15 PM (5 cycles, 7.5 h).
How much sleep do I need?
| Age | Recommended sleep |
|---|---|
| Teens (13–18) | 8–10 hours |
| Adults (18–60) | 7 or more hours |
| Adults 61–64 | 7–9 hours |
| 65 and older | 7–8 hours |
Source: CDC and the American Academy of Sleep Medicine.
Tips for better sleep
- Keep the same bedtime and wake time, even on weekends.
- Avoid screens, caffeine and heavy meals in the hours before bed.
- Loud snoring or feeling tired after a full night can be signs of sleep apnea; talk to a doctor.
Frequently asked questions
How much sleep do I need?
Adults need at least 7 hours a night; teens 8–10 hours.
What time should I go to bed to wake up at 6 AM?
8:45 PM, 10:15 PM or 11:45 PM (6, 5 or 4 cycles), allowing 15 minutes to fall asleep.
How long is a sleep cycle?
About 90 minutes on average.
About this tool
- Written by
- [Author: to be assigned]
- Reviewed by
- Expert review pending
- Last updated
- 31 Oct 2026
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