Sleep Cycle Calculator
Calculate your optimal bedtime or wake-up time based on 90-minute sleep cycles. Wake up at the end of a cycle feeling refreshed, not groggy.
Calculate Your Sleep Times
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The 90-Minute Sleep Cycle
Sleep isn't a uniform state - your brain cycles through distinct stages approximately every 90 minutes (though this can range from 80-110 minutes). Each cycle includes:
- Stage 1 (Light Sleep): The transition from wakefulness, lasting 1-5 minutes. Easy to wake from.
- Stage 2 (True Sleep): Body temperature drops, heart rate slows. Makes up about 50% of total sleep.
- Stage 3 (Deep Sleep): Also called slow-wave sleep. Hardest to wake from - this is when you feel groggy if disturbed. Critical for physical restoration.
- REM Sleep: Rapid Eye Movement sleep where most dreaming occurs. Important for memory consolidation and emotional processing.
Why Timing Matters
Waking during deep sleep (Stage 3) causes "sleep inertia" - that groggy, disoriented feeling that can last 30 minutes or more. By timing your alarm to the end of a sleep cycle, you wake during lighter sleep stages and feel more alert immediately.
How Many Cycles Do You Need?
Most adults need 5-6 complete cycles (7.5-9 hours) for optimal health. However, 4 cycles (6 hours) can work short-term. Fewer than 4 cycles regularly leads to sleep deprivation effects like impaired cognition, weakened immunity, and mood disturbances.
Our Approach
Unlike basic calculators that only show times, our Sleep Cycle Calculator provides:
- Visual sleep architecture showing your cycle breakdown
- Quality ratings for each sleep option (optimal/good/minimum)
- Smart alarm windows for flexible wake times
- Customizable cycle length (80-110 minutes) and fall-asleep time
- Age-adjusted recommendations
- Integrated power nap calculator
Disclaimer
This calculator provides general guidance based on sleep science. Individual sleep needs vary. If you consistently struggle with sleep quality despite following good sleep hygiene, please consult a healthcare provider or sleep specialist.
Help others optimize their sleep with science-backed timing.