Question 1

How does the sleep cycle calculator work?

Accepted Answer

It uses 90-minute sleep cycles. After falling asleep (average 15 min), each cycle includes light, deep, and REM sleep. Waking at the end of a cycle leaves you refreshed.

Question 2

What are the optimal sleep cycles?

Accepted Answer

4 cycles (6h) fair, 5 cycles (7.5h) good, 6 cycles (9h) ideal. Most adults need 5–6 cycles.

Question 3

Why 15 minutes sleep onset?

Accepted Answer

The average time to fall asleep is 15 minutes. The calculator adds this to bedtime before counting cycles.

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