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Sleep Cycles

Sleep science, without the homework

What time are you going to sleep?

Wake times below assume ~15 min to fall asleep · 90-minute cycles

Optimal wake-up times tap one to explore

Your sleep

14d

The science: Sleep runs in ~90-minute cycles — light sleep, deep sleep (NREM), and REM — repeating throughout the night. Deep sleep dominates the first half of the night and handles physical repair, immune function, and growth hormone release. REM dominates the second half and handles memory consolidation, emotional processing, and creativity. Waking at the end of a cycle, during light sleep, minimizes grogginess. Waking mid-cycle — especially from deep sleep — causes sleep inertia that can last 15–30 minutes.

Not medical advice. Individual cycles vary from 70–120 minutes. Consistent bedtimes matter as much as duration. This app logs only what you tell it — it can't observe sleep directly. Data stays on this device.