Douglas Almond, Yi Cheng, and Cecilia Machado examined more than 800,000 earnings reports from the U.S. unemployment insurance program during 1990 to 2010 to find how much women actually lose when they become mothers, examining different scenarios in which the motherhood penalty might be smaller. They called what they found “discouraging:” It hits all mothers in America, regardless of their pay, company, or education. 

And it happens almost instantaneously: Whereas the arrival of a firstborn child doesn’t have any effect on a man’s earnings, moms experience a 51% dock in pay, equivalent to an average of $8,000 annually. The motherhood penalty only persisted as the child aged; researchers found that six years after the first child’s birth, the pay gap between father and mother increased slightly. 

It didn’t matter if the mother worked for a woman or at a mostly woman-dominant firm. It also didn’t matter the size of the company the mother worked for. Or if she went to college. And it didn’t matter if the mother also happened to be the breadwinner in the family.

“What’s striking about the U.S. motherhood penalty is how universal it seems,” Almond tells Fortune. “Even when the female partner outearns her male partner and we might expect the lower-paid dad to ‘step up’ at home, we find a still larger motherhood penalty: around 60% of earnings.”

In Sweden, by contrast, Almond says there is no motherhood penalty when the woman outearns her male partner. “The Swedish pattern makes more economic sense—the man likely has a lower opportunity cost,” he added, referring to the country’s different cultural expectations.  

“There is a culture of U.S. dads not contributing as much childcare as in other countries,” he said, pointing to his own experience as a father. While based in New York City, his wife is Swedish and their daughters have dual citizenship in the two countries. He said he was “always struck by how few dads were at playgrounds in New York City” and the assumption that he was just “filling in.” The difference is visible in Stockholm, he said, where “you see as many dads as moms caring for their children.”

It’s this American stereotype—that child-rearing should fall on the mother—that leads to some mothers dropping out of the workforce altogether, contributing to the gap in earnings, while those who remain experience an earnings dip regardless. The effects plague women throughout their careers and beyond. 

A Harvard study found that mothers are often less likely to be hired and then usually offered lower salaries than women without children. And a survey from TIAA finds that they have almost 30% less saved for retirement than men on average, in part due to choices regarding taking care of or providing for their children.

America’s workforce continues to fail when it comes to supporting working moms, Pam Cohen, Ph.D., chief research and analytics officer at the Mom Project, told Fortune’s Ivana Pino. “The need for support extends well beyond the limited early stages of parenthood and yet tends to drop off precipitously beyond that point in time at which mothers return from parental leave,” she said. 

It doesn’t help that it’s become extremely difficult to find affordable childcare. It’s become so expensive that families spend almost a third of their household income on it. “The shortcomings of the child care system disproportionately affect the financial well-being of women, single parents, parents in poverty, families of color and immigrant families,” reads the Annie E. Casey Foundation in its KIDS COUNT Data Book, pointing to research from 2022 that showed how women were five to eight times more likely to have their careers be affected by caregiving duties in 2022. 

More affordable childcare has long been touted as a solution to the motherhood penalty in America. But that’s only half the battle. Almond believes the solution begins with changing the culture that is rooted in sexism and the way we view the roles of mother and father. “Culture can and does change,” he said.