A night of sleep is made of cycles that last about 90 minutes each. Waking up at the end of a cycle, rather than in the middle of one, usually feels easier. The calculator counts back (or forward) in steps of 90 minutes and adds the time it takes you to fall asleep, which is about 15 minutes for most people. Most adults do well on 5 to 6 cycles, which is 7.5 to 9 hours.
Most adults need 7 to 9 hours. Teenagers need more, roughly 8 to 10 hours. Six cycles equal 9 hours, five cycles 7.5 hours and four cycles 6 hours.
No. Cycle length varies from person to person and from night to night, roughly 80 to 110 minutes. Treat the times as a good starting point and adjust by how you feel in the morning.
Use the button above. It adds the time to fall asleep to the current time and lists the wake-up times after 3 to 6 full cycles.
This tool is for general information and is not medical advice.
See also: Hours Calculator · Time Zone Converter · BMR Calculator