Sleep Calculator
Find the best times to go to bed based on when you need to wake up, using 90-minute sleep cycles.
- Free to use
- No registration required
- Works on all devices
- Last updated
- 13-09-2026
Your result
23:15
5 cycles (7.5 hours)
AI explanation
Formula
Bedtime = wake-up time − minutes to fall asleep − (90 minutes × number of sleep cycles)Worked example
Wake up at 07:00, 15 minutes to fall asleep
| Field | Value |
|---|---|
| Wake-up time (24-hour) | 07:00 |
| Minutes to fall asleep | 15 |
| 6 cycles (9 hours) | 21:45 |
| 5 cycles (7.5 hours) | 23:15 |
| 4 cycles (6 hours) | 00:45 |
| 3 cycles (4.5 hours) | 02:15 |
Assumptions
- Assumes an average sleep cycle length of 90 minutes, a commonly cited approximation — actual individual cycle length varies.
- Waking at the end of a full cycle (rather than mid-cycle) is associated with feeling more rested, but individual results vary.
Frequently asked questions
How many sleep cycles should I aim for?
Most adults do best with 5-6 complete 90-minute cycles (7.5-9 hours), though individual sleep needs vary — this calculator shows several options to choose from.
Why does waking at the end of a cycle matter?
Sleep cycles move through lighter and deeper stages; waking during deep sleep (mid-cycle) often feels groggier than waking at a natural cycle boundary, when sleep is lighter.
Is 90 minutes the exact length of everyone's sleep cycle?
No — 90 minutes is a commonly cited average, but actual individual cycle length can range from about 70 to 120 minutes and may vary night to night.
I have a fixed bedtime and want to know when to wake up instead — is there a version for that?
Yes — see the Sleep Cycle Calculator, which works forward from a bedtime instead.
Why do the bedtime options seem to wrap to "the previous day"?
Since bedtimes are naturally before a wake-up time, they're shown as ordinary clock times without a date — read them as "the night before" your wake-up time.
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Related articles
Sources
- Principles and Practice of Sleep Medicine — American Academy of Sleep Medicine. Effective 01-01-2017, checked 13-09-2026.
This calculator provides a general estimate only and does not constitute personalized medical advice. If you have ongoing sleep difficulties, consult a healthcare professional.
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