How sleep cycles work

Tap any stage to learn what happens in your brain and body

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Stage 1 — Light sleep

1–7 min · Easy to wake

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You drift between wakefulness and sleep. Eyes move slowly, muscles twitch occasionally. This is when you might feel like you're falling. Your brain produces alpha and theta waves. It's easy to wake someone from this stage — they may not even believe they were asleep.

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Stage 2 — Light sleep

10–25 min · Memory consolidation

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Eye movements stop. Your heart rate slows and body temperature drops. The brain produces bursts of activity called "sleep spindles" — these are thought to consolidate memories and protect sleep from external noise. You spend about 50% of your total sleep here.

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Stage 3 — Deep sleep

20–40 min · Body repairs itself

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The hardest stage to wake from. If woken here, you'll feel groggy for 30–60 minutes — this is called "sleep inertia." Your body is hard at work: releasing growth hormone, repairing tissue, building muscle, strengthening bone, and supercharging your immune system. Deep sleep is most abundant in the first half of the night.

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REM sleep

10–60 min · Dreaming & creativity

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Your brain is as active as when you're awake — this is when vivid dreaming happens. REM stands for Rapid Eye Movement. Your body is temporarily paralysed. REM sleep processes emotions, consolidates creative memories, and is critical for learning new skills. REM periods get longer in the second half of the night — which is why cutting sleep short destroys creativity and emotional regulation.

One full cycle = ~90 minutes. You need 4–6 per night. Waking mid-cycle causes sleep inertia — the heavy, foggy feeling. Waking at cycle end feels refreshing even with fewer hours.

Nap calculator

Slide to your nap length — find out if it'll help or hurt

Nap duration 20 min

5 min120 min

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Power nap

Boosts alertness without grogginess. You won't enter deep sleep, so you wake up sharp.

Wake at:

Sleep quality quiz

5 questions to find out how well you're really sleeping

/ 10 sleep score

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Common questions

Most adults need 7–9 hours (5–6 full cycles). Teenagers need 8–10 hours. What matters most is waking at cycle end — 7.5 hours (5 cycles) often feels better than 8 hours interrupted mid-cycle.

Sleep inertia — you woke in the middle of deep sleep (Stage 3). Your brain struggles to switch gears and produces adenosine, a sleepiness chemical. This can last 30–60 minutes. Timing your alarm to end of cycle prevents this entirely.

Cycles range from 80–110 minutes. 90 is a well-researched average. Try experimenting ±15 minutes from this calculator's times to find your personal sweet spot.

Yes. Sleep before midnight contains more deep (restorative) sleep. After midnight, REM sleep increases. Consistency — sleeping and waking at the same time daily, even weekends — is the single most powerful thing you can do for sleep quality.

Average is 10–20 minutes; this calculator uses 14. Falling asleep in under 5 minutes is a sign of sleep deprivation. Taking 30+ minutes regularly may indicate insomnia — worth discussing with a doctor.