Why 90 minutes matters
Sleep runs in cycles of roughly 90 minutes, from light sleep through deep sleep into REM. Waking at the end of a cycle feels easy; an alarm in the middle of deep sleep leaves you groggy for an hour even after a long night. The times here are spaced one cycle apart, plus about 14 minutes to drift off.
Common questions
Why 90 minutes specifically?
That's the commonly cited average length of one full sleep cycle (light → deep → REM) for adults — real cycles vary roughly 70–120 minutes person to person, so treat the times as a good starting estimate, not exact.
Why add 14 minutes?
That's a typical average time to actually fall asleep after getting into bed — the calculator adds it so the suggested bedtime accounts for lying-awake time, not just the sleep itself.
For general information only — not medical advice. Talk to a doctor about anything that concerns you.