Sleep Cycle Calculator

A sleep cycle lasts approximately 90 minutes and consists of four stages: light sleep, deep sleep, very deep sleep (slow-wave), and REM (Rapid Eye Movement) sleep. A full night typically includes 4–6 complete cycles. Why timing matters: Waking up in the middle of deep sleep leaves you feeling groggy and disoriented — this is called sleep inertia. Waking up at the end of a cycle, during the lighter sleep phase, feels much more natural and refreshed. REM sleep is when most dreaming occurs and is critical for memory consolidation, emotional processing, and creativity. Deep sleep is essential for physical recovery and immune function. How much sleep do you need? Adults generally need 7–9 hours (4–6 cycles). Teenagers need 8–10 hours. Children need 9–12 hours. Quality matters as much as quantity — broken or disturbed sleep reduces time spent in restorative deep and REM stages. Tips for better sleep: Keep a consistent schedule (even on weekends), avoid screens 1 hour before bed, keep your room cool and dark, avoid caffeine after 2pm, and get morning sunlight to reset your circadian rhythm.