How it works
Sleep runs in roughly 90-minute cycles. This calculator allows 15 minutes to fall asleep, then counts back (or forward) in whole 90-minute cycles: 4 cycles = 6 hours, 5 cycles = 7.5 hours, 6 cycles = 9 hours. Waking at a cycle boundary tends to feel easier than waking mid-cycle. Most adults need 7–9 hours; this tool does not diagnose sleep problems — persistent trouble sleeping deserves a professional conversation.
Frequently asked questions
Should I always pick 5 cycles?
Not necessarily. Pick the option that gives you 7–9 hours and fits your schedule; consistency matters as much as the exact count.
Does the 15 minutes to fall asleep matter?
Yes, it is why the suggested bedtimes look 15 minutes earlier than a plain 90-minute count would give.