In a Yahoo Finance exclusive, a Fitbit data scientist and Fitbit’s lead sleep research scientist discussed findings from their analysis of data from 6 billion nights of its customers’ sleep. In March 2017 Fitbit launched a new Sleep Stages feature that uses accelerometer data, heart rate variability, and algorithms to estimate how long users spend in each stage of sleep.

The analysis found that women sleep longer each night than men. While women average six hours and 50 minutes of sleep a night, men get only six hours and 26 minutes of sleep. Both averages fall short of the AASM sleep duration recommendation that adults should sleep 7 or more hours per night for optimal health.

The data show that the average American goes to bed at 11:21 p.m. The analysis also found that bedtime variability during the week was associated with reduced sleep duration.