Sleep Calculator

Find the ideal bedtime or wake-up time based on 90-minute sleep cycles

Sleep Cycle Calculator
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Select one or more cycle counts to see those times highlighted

From the Blog

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How Sleep Works — Cycles, Stages & How to Wake Up Refreshed
What happens in each sleep stage and how to calculate your perfect bedtime.
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How the Sleep Calculator Works

Sleep happens in repeating 90-minute cycles. Each cycle moves through four stages — from light sleep into deep slow-wave sleep and back up through REM sleep. Waking at the end of a cycle, when sleep is naturally lightest, minimises grogginess and sleep inertia.

The calculator adds 15 minutes for the average time it takes to fall asleep, then counts back (or forward) in 90-minute intervals to show you the optimal times.

N1 — Light Sleep
Transition to sleep. Easy to wake. Lasts 1–5 minutes. Muscles may twitch.
N2 — Core Sleep
Heart rate slows, body temperature drops. Memory consolidation begins. ~25 min.
N3 — Deep Sleep
Hardest to wake from. Body repairs tissue and boosts immunity. ~20–40 min.
REM — Dream Sleep
Brain is active. Emotional processing and creativity. Cycles get longer through the night.

Disclaimer: CalculatorXP health calculators are for informational purposes only and do not constitute medical advice. Sleep needs vary between individuals. If you have persistent sleep difficulties, consult a healthcare professional.