Explore sleep deeper

Four specialized tools to fine-tune your rest.

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Nap Calculator

Smart nap timing with time-of-day awareness

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Cycle Visualizer

See REM and deep sleep stages through the night

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Caffeine Timer

Watch caffeine decay before your bedtime

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Sleep Debt Tracker

Calculate your sleep debt and get a recovery plan

The Science

Why sleep cycles matter

Your body cycles through distinct stages. Waking at the right moment changes everything.

Circadian Rhythm

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.

90-Minute Sleep Cycles

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.

Deep Sleep — Body Restoration

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 — Mind Processing

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.

Learn More

Sleep science deep dives

Evidence-based articles to help you understand and improve your sleep.

Sleep Calculator