Sleep
Sleep Cycle Calculator
Find the best time to sleep or wake up based on 90-minute sleep cycles — so you wake up refreshed, not groggy.
Quick Answer
Sleep cycles last about 90 minutes. To wake up feeling rested, aim to complete 5–6 full cycles (about 7.5–9 hours), plus 15 minutes to fall asleep.
How sleep cycles work
Each night your brain moves through repeating stages: light sleep, deep (slow-wave) sleep, and REM sleep. Together, these stages form one sleep cycle that lasts around 90 minutes.
Waking up in the middle of deep sleep is what causes that heavy, groggy feeling known as sleep inertia. Waking at the end of a cycle — when you're in light sleep — feels much more natural.
Key Fact
One full sleep cycle lasts about 90 minutes, and most adults need 4–6 cycles per night.
Consistency matters more than perfection. Going to bed and waking up at similar times each day helps your body align its cycles with the clock.
FAQ
How long is one sleep cycle?
A full sleep cycle averages 90 minutes, moving through light sleep, deep sleep, and REM. Most adults need 4–6 complete cycles per night.
Why does 15 minutes get added?
Research suggests the average healthy adult takes about 10–20 minutes to fall asleep. We use 15 minutes as a reasonable baseline.
Is it better to wake up between cycles?
Yes. Waking at the end of a cycle (in light sleep) usually feels less groggy than being pulled out of deep sleep or REM.
Medical disclaimer
Wellenziah content is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of your doctor or other qualified health professional with any questions you may have regarding a medical condition.