On Wednesday, NerdWallet released a study that found women in Wyoming make a mere 64 cents for every $1 a local man earns. That’s about 16 cents below the national average of 80 cents for every man’s $1, according to 2015 U.S. Census Bureau data. But according to the study, this wage gap in Wyoming and elsewhere is also creating a bigger divide when it comes to a 401(k) and traditional individual retirement accounts, or Roth IRA.

Women in Wyoming must tuck away $1.55 for every $1 a man invests in retirement savings in order to build an equivalent nest egg, researchers found—about 30 cents more than the $1.25 average American woman need to save for every $1 a man invests.

To conclude those numbers, NerdWallet examined U.S. Census Bureau data from 2007 and 2015 to determine how annual income and wages changed over that time frame. The study’s authors also charted the states that have seen the pay gap shrink during that period, and also calculated where it has worsened.

New York, Rhode Island, Delaware, New Hampshire, and Connecticut all saw the pay gap shrink, with New York (on average) boasting the smallest difference in wages. As of 2015, women in New York made about 89 cents for every $1 a man earned—meaning they have to invest $1.13 for every $1 a man saves to reach the same size retirement as their male counterparts, the study found.

Though Oklahoma was better than Wyoming when it came to the wage gap, it was the worst state for wage gap improvement during the same time period (2007-2015), according to NerdWallet. Women in that state would need to save $1.37 for every $1 men save there.

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So, what’s causing the wage gap? Instead of “equal pay for equal work,” the issue may be described as “equal pay for equal value.” In other words, the gap in wages is most likely a result of “the clustering of men in higher-paying positions and professions,” the researchers wrote in the study—a problem that is perpetuated by the fact women are far more likely to take career breaks for child and elder care, thus limiting the number of women working in time-consuming jobs with little flexibility for family needs, according to the 2014 Harvard study NerdWallet references.

When it comes to saving for retirement, there’s no question that both men and women have a hard time saving: About half of U.S. families aren’t saving enough to maintain their standard of living once they’ve retired, notes the study. But the issue becomes a bigger challenge for women, as they, on average, live five years longer than men.