Sleep Calculator
Wake up feeling refreshed by timing your sleep to complete full 90-minute cycles. Calculate the best bedtimes for a given wake-up time, or the best wake-up times if you go to bed now.
How Sleep Cycles Work
Sleep comes in cycles of roughly 90 minutes, each containing multiple stages: light sleep (N1/N2), deep sleep (N3), and REM (Rapid Eye Movement) sleep. Waking mid-cycle — especially during deep sleep — causes sleep inertia: the groggy, disoriented feeling that can last 30–60 minutes.
By timing your alarm to the end of a complete cycle, you wake naturally from light sleep and feel alert immediately.
| Cycles | Total Sleep | Recommended For |
|---|---|---|
| 4 cycles | 6 hours | Short-term only — minimum viable sleep |
| 5 cycles | 7.5 hours | Most adults — good alertness and recovery |
| 6 cycles | 9 hours | Teenagers, athletes, recovery days |
Frequently Asked Questions
About This Sleep Calculator
This free sleep calculator suggests optimal bedtimes or wake-up times based on 90-minute sleep cycles. Enter when you want to wake up to find the best times to fall asleep, or enter your bedtime to find the ideal wake-up times.
Sleep occurs in 90-minute cycles moving through light, deep, and REM stages. Waking up at the end of a complete cycle — rather than in the middle of deep sleep — reduces sleep inertia and makes you feel more alert in the morning.
When to use this calculator
- Finding a bedtime that avoids waking up mid-cycle
- Calculating how many complete sleep cycles fit in your schedule
- Planning sleep around an early morning event or flight
- Understanding why some mornings feel worse than others
Standards & References
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