The Science of 90-Minute Sleep Cycles

Waking up refreshed isn't about the total number of hours you spend in bed; it is about the neurological state your brain is in when the alarm goes off. Human sleep is governed by 90-minute segments. During these cycles, your brain moves from light sleep to the restorative Deep Sleep, and finally into REM.

If you wake up in the middle of a deep sleep phase, you experience **Sleep Inertia**. Our Sleep Cycle Calculator predicts the "Sleep Window" at the end of a REM cycle, allowing you to glide into consciousness naturally.