Here's the real reason women get smarter about money as they get older

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While a majority of Americans have trouble understanding basics about money, women tend to perform less well on financial literacy tests than men, according to researchers. But at a certain point in their lives, the vast majority of women catch up.

It's for a sobering reason, though: Because they realize their husbands are going to die.

In a report by economists Annamaria Lusardi and Olivia Mitchell, only about 34 percent of people surveyed could correctly answer three questions about how to save in bank accounts and invest in stocks. When the data is broken out by gender, women scored lower than men.

"We do see that women's financial literacy needs some work," says Mitchell, the executive director of the pension research council at The Wharton School at the University of Pennsylvania.

One reason for the information gap is because men usually handle financial responsibilities in households, Mitchell tells CNBC Make It. Then the prospect of a death in the relationship shifts the calculus.

"Typically, since women marry men older than they are, their husbands die before they do," she says. "So what we can see as time marched forward, is that the women tended to start out as less financially literate — but as the day approached where their husband passed away, the women gained financial skills."

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Mitchell cites a study by Joanne Hsu, an economist at the Federal Reserve, which looks at spousal relationships and money. Hsu found that, by the time their husbands die, 80 percent of women are as financially literate as men.

As independence approaches, the study found that women are more likely to follow the stock market and report increased financial skills. One reason for the better focus could be that retirement is increasingly left to people to manage for themselves.

"Having sufficient financial literacy is becoming even more important since the responsibility for retirement planning has shifted to individuals," states Hsu's report.

Overall, the findings suggest that "the gender gap in financial literacy may reflect strategic responses of women to incentives over the life cycle."

While Hsu's report agrees that studies show women generally have less financial knowledge than men, it's not because they're less intelligent. Many heterosexual, partnered women rely on their husbands to make financial decisions as part of a traditional distribution of labor. Then, when women realize they have to take care of themselves, they do.

The study concludes that "women do indeed increase their financial knowledge on a number of dimensions as their husbands age."

For Mitchell, the trend underlines that women are as capable as men of learning about money.

"It shows that women can do it, that they are teachable," Mitchell says. "It is just that, until they need to, they don't necessarily invest in that information."

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