Sleep Calculator

Calculate optimal sleep and wake times based on 90-minute sleep cycles. Wake up feeling refreshed by completing full cycles.

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Understanding Sleep Cycles

Sleep isn't a uniform state - your brain cycles through different stages throughout the night. Each complete sleep cycle takes approximately 90 minutes and includes:

Sleep Stages Breakdown

  • Light Sleep (N1 & N2): The transition from wakefulness to sleep. Your heart rate slows and body temperature drops. Makes up about 50% of total sleep.
  • Deep Sleep (N3): The most restorative stage. Your body repairs tissues, builds bone and muscle, and strengthens the immune system. Makes up about 20% of sleep.
  • REM Sleep: When most dreaming occurs. Important for memory consolidation and emotional regulation. Increases in later cycles, making up about 25% of sleep.

Why 90-Minute Cycles Matter

Waking up during deep sleep or REM can cause "sleep inertia" - that groggy, disoriented feeling. By timing your sleep to complete full cycles, you wake during lighter sleep and feel more refreshed.

Optimal Sleep = (Number of Cycles x 90 minutes) + 15 minutes to fall asleep

Recommended Sleep Duration

  • 4 cycles (6 hours): Minimum recommended - use only when necessary
  • 5 cycles (7.5 hours): Good for most adults - meets minimum recommendations
  • 6 cycles (9 hours): Optimal for recovery and peak performance

Note: Individual sleep needs vary. Some people feel great on 7 hours while others need 9. Pay attention to how you feel and adjust accordingly. This calculator provides guidelines based on average sleep cycle duration.