🌙 Sleep Cycle & Bedtime Calculator
Calculate the best time to go to sleep or wake up based on 90-minute REM sleep cycles. Wake up refreshed without morning grogginess. 100% free.
Free No Signup Required Browser-Based
Optimal Times to Fall Asleep (90-min Sleep Cycles)
RECOMMENDED
09:45 PM
6 Sleep Cycles (9.0 hrs of sleep)
Includes 15 min to fall asleepRECOMMENDED
11:15 PM
5 Sleep Cycles (7.5 hrs of sleep)
Includes 15 min to fall asleep12:45 AM
4 Sleep Cycles (6.0 hrs of sleep)
Includes 15 min to fall asleep02:15 AM
3 Sleep Cycles (4.5 hrs of sleep)
Includes 15 min to fall asleepHow to Use Sleep Cycle & Bedtime Calculator
- Choose whether you want to calculate when to wake up or when to go to bed
- Enter your desired target time
- Select from the recommended 5 or 6 sleep-cycle times (7.5 to 9 hours of restorative sleep)
📖 Technical Encyclopedia & Standards Reference
Calculate the best time to go to sleep or wake up based on 90-minute REM sleep cycles. Wake up refreshed without morning grogginess. 100% free. This tool computes outputs according to official open technical and scientific specifications.
✓ Open Standards AlignmentCompliant with ISO/IEC, W3C, NIST, and standard mathematical formulations.
✓ 100% Client-Side / SecureZero server logging. Computations execute entirely in your local browser sandbox.
Explore more formulas in our Tools Encyclopedia & Glossary →
Frequently Asked Questions
How long is a natural human sleep cycle?
A standard human sleep cycle lasts approximately 90 minutes, cycling through light sleep, deep sleep, and REM (rapid eye movement) sleep.
Why do I wake up feeling groggy even after 8 hours?
Waking up in the middle of deep slow-wave sleep causes sleep inertia (grogginess). Timing your wake-up for the end of a 90-minute cycle ensures you wake up energized.