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Choosing to start a family can be one of the most costly career decisions a woman can make. That's one of the big takeaways from a new set of data on the gender-based wage gap, released Thursday by PayScale.

The pay gap between a single, childless woman and her similar male colleague is 0.6%, after controlling for factors like years of experience, education, skills, management responsibilities, and company size — the smallest of any male-female peer groups. (That means for every $10,000 a single, childless man makes, a comparable woman would make $9,940.)

But that adjusted pay gap grows seven times larger when you compare the earnings of married men and women who have kids, according to PayScale, which collected data on 1.4 million full-time employees between July 2013 and July 2015. And when the report compared median earnings for workers who were married with children without controlling for any factors, the wage gap for women was a whopping 31.1%.

The second-greatest adjusted wage gap between peers (1.6%) was that between married women and men without children, suggesting that marriage itself -- and not just having children -- is correlated with greater pay inequality. Unmarried women, either with or without children, fare much better than married women do when compared with their single male counterparts.

By contrast, men actually benefit from marrying and beginning a family. PayScale's median salary data shows both the "motherhood penalty" and "fatherhood bonus": Married men with children get the highest pay among male earners ($67,900), but the biggest salary among women ($48,300) goes to married women without children.

This finding backs up a study published last year by Michelle Budig, a sociology professor at University of Massachusetts, Amherst, which found that men's earnings increased more than 6% on average when they had at least one child, while women's pay decreased 4% for each child they had.

That same study found that employers are more likely to see fathers and married men as more stable and committed to work, since they have a family to provide for, while women face the perception that having a family will make them work less and become more distracted.

PayScale's report also found that the more often workers say they put family above work, the larger the controlled gender pay gap becomes. The earning gap between married mothers and fathers who say they put family above work obligations at least once a year is 4.4%, but that gap was halved between married mothers and fathers who say they never put family obligations above work.

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