# Sleep cycle

A sleep cycle is one pass through the stages of sleep, light, deep and REM, lasting roughly 90 minutes on average.

Cycles vary between about 70 and 120 minutes. Waking at the end of one can feel easier, which is why bedtime calculators count in 90-minute steps.

Related: [Sleep debt](https://revns.com/dictionary/sleep-debt.md), [Circadian rhythm](https://revns.com/dictionary/circadian-rhythm.md)

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