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Circadian Rhythm Lab

Precision sleep timing. Calculate your 90-minute sleep cycles to wake up feeling refreshed and energized.

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Wakeup Time

Set your target morning alarm

Time to Fall Asleep

Duration14 mins

The average person takes 14 minutes to fall asleep. Adjust this to match your habits.

Optimized for Human Biology. Zero Data Collection.

Master Your Sleep Cycles

Ever wake up feeling groggy even after a long night of sleep? This is often caused by sleep inertia—the result of being woken up in the middle of a deep sleep cycle. Our Sleep Cycle Calculatorhelps you time your wake-up or bedtimes to align with your body's natural 90-minute rhythms.

A typical human sleep cycle lasts about 90 minutes. During this time, you move through various stages of sleep, from light sleep to deep sleep and REM (Rapid Eye Movement). Waking up at the end of a cycle, when you are in the lightest stage of sleep, allows you to feel refreshed and alert immediately.

Most adults need 7 to 9 hours of sleep (5 to 6 cycles) to function optimally. However, even getting 6 hours (4 cycles) can feel better than 7 hours if you wake up at the right time. Our tool also accounts for Sleep Latency—the time it takes for you to actually fall asleep once your head hits the pillow.

Sleep Hygiene Tips

Frequently Asked Questions

The 90-minute rule suggests that human sleep consists of roughly 90-minute cycles. By timing your sleep to end at the completion of a cycle, you avoid waking up during deep sleep, which significantly reduces morning grogginess.
While 5 or 6 cycles (7.5 to 9 hours) are considered optimal for most adults, consistency is key. Getting 4 cycles (6 hours) at the same time every day is often better than erratic sleep patterns.
Sleep inertia is the feeling of grogginess and disorientation experienced upon waking. It is most severe when you wake up during a stage of deep (slow-wave) sleep.
Improve your sleep latency by cooling down your room, avoiding blue light (screens) 60 minutes before bed, and maintaining a consistent 'wind-down' routine.
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