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Sleep Cycle Calculator

Sleep happens in 90-minute cycles. Waking up between cycles (rather than in the middle of one) helps you feel more rested. This tool calculates the best times based on complete sleep cycles, plus ~15 minutes to fall asleep.

What time do you need to wake up?

💤 Sleep & Mental Health

Poor sleep is both a symptom and a driver of anxiety and depression. Adults need 7–9 hours per night. If you're consistently sleeping poorly and it is affecting your mood, it is worth mentioning to your GP — sleep issues are very treatable.

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v9.6
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About this tool

Based on
~90-minute sleep cycle research (Kleitman)
Calculates
Ideal bed/wake times by full cycles
Good for
Reducing grogginess from mid-cycle waking
Diagnostic?
No — not a substitute for a sleep study

Common Questions About the Sleep Cycle Calculator

What is the science behind 90-minute sleep cycles?
Sleep occurs in cycles of roughly 90 minutes, alternating through light sleep, deep sleep, and REM sleep — a pattern of ultradian rhythm first described by sleep researcher Nathaniel Kleitman. Waking near the end of a cycle, rather than mid-cycle, is generally associated with feeling less groggy.
Is this calculator a substitute for a sleep study?
No. It's a simple planning tool based on average cycle length — actual cycle length varies between individuals and across a night. If you have ongoing sleep problems, our insomnia support page and CBT-I information are a better starting point than timing alone.
Is my sleep data stored anywhere?
No — this calculator works entirely in your browser with no data saved or sent anywhere.
Medical disclaimer: This site provides general health information and verified helpline numbers only. It is not a substitute for professional medical advice, diagnosis, or treatment. If you are in immediate danger, call 000. For mental health crisis support, call Lifeline 13 11 14. Always seek the advice of a qualified health professional with any questions regarding a medical condition. Helpline numbers verified June 2026. No AI-generated content is used on this site.
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