One reason men make more money than women is because they work so much overtime.

The gender gap in pay persists due to the fact that men are more likely than women to work 50 hours-plus a week, found a recent study (pdf) published by the American Sociological Review. The extra hours—known as “overwork”—result, on average, in an extra 6% in hourly wages across all occupations. This difference has exacerbated the gender pay gap by around 10%, the study claims.

In 2000, 19% of men worked 50 hours or more per week, compared to 7% of women. The researchers suggested that women are less likely both to enter a job that demands overworking and to stay in it. And despite moves toward equality, women still tend to be more responsible than men for housework and childcare—hours that hardly count on the job but make them plenty overworked, too.

Indicating a willingness to work longer hours is one of the most effective ways men can increase their salaries, a 2011 report found, but it had no effect on women’s income or corporate progression.

Overwork is considered necessary to move up the corporate ladder, and indeed, the study found overworkers are more prevalent in professional and managerial positions. Researchers attribute the higher wages to employers’ perception that overworkers have contributed more to a company’s bottom line, or the impression that they tend to work harder and more productively.