How this sleep calculator works
Sleep happens in cycles that last roughly 90 minutes. Many people feel less groggy when they wake up at the end of a cycle instead of in the middle of one. This calculator counts back (or forward) in 90-minute cycles and adds the time it usually takes you to fall asleep.
Cycle length varies from person to person and night to night, so treat these times as a guide. If you wake up tired, try moving your bedtime 15 minutes earlier or later.
How much sleep do adults need?
Health guidelines generally recommend that adults get at least 7 hours of sleep a night. Five or six 90-minute cycles (7½ or 9 hours) fit that well.