The average adult human takes fourteen minutes to fall asleep. Sleep cycles typically last 90 minutes. Waking up in the middle of a sleep cycle leaves you feeling tired and groggy, but waking up in between cycles lets you wake up feeling refreshed and alert.
The Bedtime Calculator tells you when it's a good time to fall asleep, based on when you have to wake up. The calculator works by counting backwards in sleep cycles.
(thanks Cora)The Presurfer
