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How it works
What is a sleep cycle?
A sleep cycle is one full pass through the stages of sleep — from light sleep into deep sleep and REM, then back. Each cycle lasts about 90 minutes, and a healthy night usually contains 4 to 6 of them.
Why 90 minutes?
90 minutes is the average length of a complete cycle for most adults. Waking up at the end of a cycle, rather than in the middle of deep sleep, helps you feel alert instead of groggy.
How many cycles do I need?
Most adults feel best with 5 cycles (about 7.5 hours). 4 cycles works in a pinch, and 6 cycles can feel like too much. Quality matters as much as quantity.
Does the 14-minute fall-asleep time apply to everyone?
It's an average. Some people drift off in 5 minutes, others take 30. Adjust mentally if you know your own pattern — SleepClock uses 14 minutes as a sensible default.