Find your optimal sleep times. Based on 90-minute cycles. Free, private, instant.
Three specialized tools to fine-tune your rest.
Smart nap timing with time-of-day awareness
See REM and deep sleep stages through the night
Watch caffeine decay before your bedtime
Calculate your sleep debt and get a recovery plan
Your body cycles through distinct stages. Waking at the right moment changes everything.
Your body runs on a 24-hour internal clock. Morning light and evening darkness trigger hormonal shifts that tell you when to sleep and when to wake. Consistency keeps this rhythm sharp.
Sleep isn't one long state — it's a sequence of ~90-minute cycles. Each moves from light sleep into deep sleep, then REM. Waking up mid-cycle, especially during deep sleep, causes the groggy feeling called sleep inertia.
During deep sleep, your body releases growth hormone, repairs tissue, builds bone and muscle, and strengthens your immune system. This stage dominates the first half of the night and is the hardest to wake from.
REM sleep handles memory consolidation, emotional regulation, and creative problem-solving. REM periods lengthen through the night — your longest REM happens right before you naturally wake up.