Half of U.S. mothers report having no retirement savings, according to a new analysis from the Century Foundation using ​​data from the Financial Health Network. That’s compared to only about 32% of fathers who report a lack of savings, and 39% of Americans without children. 

Mothers disproportionately shoulder society's care work, points out the report’s author, Laura Valle Gutierrez: “Our retirement system is based on lifelong earnings and work, but our work systems and our economy really are relying on the unpaid and undervalued work of women and mothers specifically,” she says. “Mothers are the ones that are paying a penalty for the status quo.”

Women generally face more threats than men do to their long-term financial security, but those challenges are compounded for women with children, the report finds. Not only do mothers face the gender wage gap—women still earn $0.83 for every dollar men make in 2023—but they also face a “motherhood penalty” when it comes to hiring, salaries, and perceived competence. “Mothers are also paid less for each child that they have, which impacts how much discretionary income they have to save,” Valle Gutierrez tells Fortune.

That penalty can be attributed, at least in part, to women taking on more of the childcare responsibilities than men. Pew Research Center recently reported that married women tend to spend more time on household chores and childcare, while husbands spend more time on leisure activities. Unequal caregiving labor results in an average $400,000 loss in lifetime earnings for women over the course of a 40-year career, according to research by the National Women's Law Center (NWLC). Black women generally experience a loss of $1 million in lifetime earnings. 

And children are not the only people women are caring for. Among those Americans regularly assisting elderly parents and those with special needs, about 61% are women. And the majority of caregivers have reported their responsibilities have resulted in missing work. 

In the U.S., retirement savings are tied to work—from employer-sponsored accounts such as 401(k)s to the Social Security Administration’s work history calculations. The average Social Security benefit for women is nearly $5,000 less than it is for men ($20,050 vs $15,379 per year for women). Social Security payments are calculated based on a worker's highest 35 years of earnings and the age retirement benefits start—but less than half of women with children have 35 years or more of work experience.

That leaves many women financially vulnerable in their twilight years. About 16% of women aged 65 and older live in poverty, compared to just 12% of similar-age men, according to a separate 2021 report by the NWLC and the Center on Poverty and Social Policy. Women also tend to live longer than men, and many have higher healthcare expenses as they age. That makes a healthy retirement nest egg even more critical.

In earlier eras, where men were more likely to be the primary breadwinners of their families, their pensions or retirement savings were expected to provide for their partners as well as themselves—which often left women in a precarious position, financially. Now a higher percentage of women receive benefits based on their own earnings. For many, including single women, this has led to more economic freedom in retirement, but mothers still face a shortfall compared with fathers and non-parents.

The COVID-19 pandemic brought the disparities for mothers into focus, Valle Gutierrez says. When schools and daycares shut down across the country, 865,000 women left the workforce. But even among those mothers who managed to juggle their jobs and their childcare responsibilities, there were consequences—typically in terms of their job mobility. Many mothers reduced their work hours or switched to a different job that provided more flexibility. 

“All of these choices that women and mothers make to manage their care responsibilities can have outsize effects on wages down the line, reducing the possibilities for promotions, and just lowering lifetime earnings overall,” Valle Gutierrez says. 

The result, Valle Gutierrez says, is bleak: “Moms are heading into retirement just really underprepared.”