Sleep Calculator
This Sleep Calculator helps you find the best times to go to bed or wake up based on natural 90-minute sleep cycles. Waking at the end of a complete cycle helps you feel refreshed rather than groggy, even with less total sleep.
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Enter your details
Recommended Bedtimes
ExampleExample figures, not your own. Worked for a 6:30am wake time and 15 minutes to fall asleep. Enter your own details and press Calculate.
9:15 pm
6 cycles · 9h of sleep
10:45 pm
5 cycles · 7.5h of sleep
12:15 am
4 cycles · 6h of sleep
1:45 am
3 cycles · 4.5h of sleep
Times include 15 minutes to fall asleep.
How It Works
Sleep occurs in 90-minute cycles, each progressing through light sleep, deep sleep, and REM sleep. Most people take about 15 minutes to fall asleep. This calculator adds the fall-asleep time to multiples of 90 minutes (4, 5, or 6 complete cycles) to recommend optimal bed or wake times. Waking between cycles, rather than mid-cycle, reduces sleep inertia and grogginess.
How to use it
- 1Choose whether you want to calculate bedtime or wake time
- 2Enter your target wake-up time or the time you plan to go to bed
- 3Optionally adjust the time it takes you to fall asleep (default 15 minutes)
- 4Click "Calculate" to see your optimal sleep schedule
- 5Choose from 4-cycle (6h), 5-cycle (7.5h), or 6-cycle (9h) options
Quick Reference
| Sleep Cycles | Duration | Total Sleep | Rating |
|---|---|---|---|
| 3 cycles | 4.5 hours | 4h 30m | Minimum |
| 4 cycles | 6 hours | 6h 00m | Adequate (short-term) |
| 5 cycles | 7.5 hours | 7h 30m | Optimal |
| 6 cycles | 9 hours | 9h 00m | Optimal (recovery) |
| 7 cycles | 10.5 hours | 10h 30m | Excessive for most adults |
Each cycle is approximately 90 minutes. Actual cycle length varies from 80 to 110 minutes between individuals.
How This Is Calculated
- cycles
- = number of complete sleep cycles (3-6)
- 90 min
- = average length of one sleep cycle
- fall-asleep time
- = minutes to fall asleep (default 15)
Sleep cycle length varies between individuals (80-110 minutes). The 90-minute average works well for most people. Adjust your fall-asleep time if you know it differs from the 15-minute default.