Free Online Sleep Cycle Calculator
Find the Best Bedtime or Wake-Up Time Based on Sleep Cycles
Need to use Sleep Cycle Calculator right now?
Waking up mid-sleep-cycle — during deep sleep rather than a lighter phase — is a major reason people feel groggy even after a seemingly adequate number of hours in bed, since sleep moves through roughly 90-minute cycles and waking between cycles rather than in the middle of one tends to feel noticeably more refreshing.
Recommended bedtimes
9:45 PM
6 cycles (9.0h sleep)
11:15 PM
5 cycles (7.5h sleep)
12:45 AM
4 cycles (6.0h sleep)
2:15 AM
3 cycles (4.5h sleep)
Based on ~90-minute sleep cycles plus 15 minutes to fall asleep — waking up between cycles (rather than mid-cycle) tends to feel less groggy.
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Features
- Runs entirely in your browser
- Privacy-first — your data is never uploaded
- Real-time, instant results
- 100% free, no sign-up required
- Works on desktop, tablet, and mobile
- No installation needed
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About Sleep Cycle Calculator
Waking up mid-sleep-cycle — during deep sleep rather than a lighter phase — is a major reason people feel groggy even after a seemingly adequate number of hours in bed, since sleep moves through roughly 90-minute cycles and waking between cycles rather than in the middle of one tends to feel noticeably more refreshing.
This calculator works in either direction: tell it when you need to wake up, and it counts backward in whole 90-minute cycles (plus the typical 15 minutes it takes to fall asleep) to suggest several possible bedtimes; or tell it when you're going to bed, and it counts forward to suggest several wake-up times, each aligned to a whole number of sleep cycles.
Each suggested time shows how many cycles and total hours of sleep it represents, letting you pick a time that balances getting enough sleep against your actual schedule constraints.
How it works
- Choose your mode. Select whether you're setting a wake-up time or a bedtime.
- Enter the known time. Input the wake-up time or bedtime you already know.
- See suggested times. View several options aligned to whole sleep cycles.
Examples
Need to wake up at 7:00 AM
Input
Mode: wake-up time, Time: 7:00 AM
Output
Suggested bedtimes include 9:45 PM (6 cycles) and 11:15 PM (5 cycles)