The Science of 90-Minute Sleep Cycles

This calculator is based on the idea that humans sleep in natural cycles of approximately **90 minutes**. Waking up in the middle of a sleep cycle often leads to grogginess and feeling tired, even if you slept for a long time. This is known as **sleep inertia**.

How It Works:

• **The 14-Minute Rule:** The calculation includes a **14-minute average latency period**—the time it takes for a typical adult to fall asleep.
• **Optimal Cycles:** The calculator suggests times based on completing 5 or 6 full 90-minute cycles (7.5 hours or 9 hours of total sleep), as these are the most common recommended durations.
• **Wake-Up Phase:** By timing your wake-up for the end of a complete cycle, you are more likely to be in a lighter stage of sleep (Stage 1 or 2), resulting in a much more refreshed and energized start to your day.

Disclaimer: This tool provides suggestions and is not a substitute for professional medical advice. Individual sleep needs vary.