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.
Worked example
To wake at 7:00 after 90-minute cycles, typical bedtimes are about 11:00, 12:30, or 9:30 the night before, plus ~15 minutes to fall asleep. Five cycles is 7.5 hours of sleep.
Cycle length is not exactly 90 minutes for everyone. Shift work, caffeine, and a new baby blow up the chart. This is a schedule sketch, not a sleep clinic. Not medical advice.
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.