90-minute cycles
A common sleep-hygiene trick is to wake at the end of a ~90-minute cycle instead of in the middle of deep sleep. This page adds 15 minutes to fall asleep, then counts 4–6 cycles (6–9 hours). It is a planning aid, not a diagnosis of insomnia or sleep apnea.
Common questions
Do cycles last exactly 90 minutes?
No. They vary. 90 minutes is a popular average.
How much sleep do adults need?
Many adults do well near 7–9 hours. Follow how you feel and a clinician’s advice.