Sleep Calculator
Find the best times to sleep or wake up based on 90-minute sleep cycles. Waking between cycles helps you feel more refreshed.
Overview
Sleep proceeds in cycles of roughly ninety minutes, each moving through light sleep, deep slow-wave sleep and REM. Waking at the end of a cycle, when sleep is lightest, produces less grogginess than waking mid-cycle from deep sleep. Working backwards from a fixed wake time in ninety-minute steps, with about fourteen minutes allowed for falling asleep, yields bedtimes that align with cycle boundaries.
Go to bed at Wake up at
cycles
hours
How Sleep Cycles Work
| Cycles | Sleep Time | Total (incl. 14 min to fall asleep) |
|---|---|---|
| 6 | 9h 0m | 9h 14m |
| 5 | 7h 30m | 7h 44m |
| 4 | 6h 0m | 6h 14m |
| 3 | 4h 30m | 4h 44m |
Sleep Tips
- Each sleep cycle lasts about 90 minutes.
- It takes an average of 14 minutes to fall asleep.
- Most adults need 5-6 complete cycles (7.5-9 hours) per night.
- Waking up between cycles helps you feel more refreshed.
How to Use
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1
Enter your values
Type your numbers into the Sleep Calculator input fields.
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2
Adjust the options
Choose the units, method, or region that fits your situation, or apply a quick preset.
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3
Read the result instantly
The result updates as you type — no submit button, and nothing is sent to a server.
About
Cycle length is an average rather than a constant. Individual cycles range from about seventy to a hundred and twenty minutes and lengthen across the night as REM periods extend, so the alignment is approximate and drifts by the later cycles. Sleep inertia — the impaired alertness that follows waking from deep sleep — is the effect the timing tries to avoid.
Total duration still dominates. Most adults require seven to nine hours, and five well-aligned cycles do not substitute for the sleep debt accumulated by habitually short nights.