We hypothesized that the coefficient of variation in sleeping time for a week is an effective evaluation index for social jetlag. The purpose of the present study was to indicate the relationship between variation in sleeping time for a week, chronotypes, and difference in the median of sleep between weekdays and free days (previous indicators for social jetlag). A total of 1,000 young men volunteered to participate in this study. The participants recorded their time of waking up and going to bed for a week. In addition, the duration of sleep and the coefficient of variation for sleeping time for a week were calculated. The chronotype was measured using the Munich chrono type questionnaire (MCTQ)-Japanese version. We observed a significant relationship between the difference in the median of sleep time between weekdays and free days and variation in the time of waking up, going to bed, and sleeping, for a week. It was suggested that social jetlag may be caused not only by the to sleep in weekends days, but also by irregularities in time of waking up and going to bed. Therefore, the coefficient of variation of sleeping time may be an evaluation index for social jetlag, considering the variation in sleeping time on weekdays. These data suggested that the coefficient of variation in sleeping time for a week, combined with weekdays and free days, may potentially be used as an index to evaluate social jetlag.