Today, men out-earn women in every country on earth. Economists estimate that the U.S. gender pay gap — the gap between the median salaries of all working men and women in the U.S. — is about 80 cents earned by women for every dollar earned by a man.

Many factors drive the gender pay gap, but one of the most common explanations is the so-called "motherhood penalty," or the way that women's earnings are negatively impacted by raising children, while men's earnings are not. According to an analysis of Census data by the non-profit National Women's Law Center, mothers in the U.S. are paid 71 cents for every $1 fathers make — about $16,000 a year in lost wages.