How to Use the Sleep Cycle & 90-Minute REM Wakeup Calculator
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Select whether you want to calculate wake times if you go to sleep right now, or find the best bedtime for a specific target wakeup hour.
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The tool factors in the average 14 minutes it takes a human to fall asleep.
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Pick from optimal 5-cycle (7.5 hours) or 6-cycle (9 hours) wakeup times.
Practical Example & Use Case
Common Real-World Scenario
If going to bed at 11:00 PM, choosing a wake-up time of 6:44 AM (5 full 90-minute cycles) so your alarm rings at the lightest phase of sleep.
Technical Notes & Limitations
Browser Engine Architecture
Based on standard physiological sleep architecture research.
Frequently Asked Questions
Why do I feel exhausted after 8 hours of sleep?
Waking up in the middle of deep Stage 3/4 slow-wave sleep causes severe 'sleep inertia'. Completing a full 90-minute cycle ensures you wake up from light sleep.