Do you really know how much your spouse earns?

In the constant struggle to balance family finances, many Americans have a problem: They don't really know how much money their spouses are bringing home. In a study of 1,051 couples, Fidelity Investments asked people how much their partner earns. More than 40% got the question wrong. One in 10 misjudged their partner's income by more than $25,000. So far the 21st century hasn't exactly been easy on middle-class finances, and couples' failure to communicate may be adding to the anxiety. If you don't have a handle on how much your household earns, it can be hard to feel in control of your spending. Fidelity also found that more than half of people worry about outliving their retirement savings, up from 42% in 2013. Couples' ignorance about their incomes seems to be growing, from 27% in 2013 to 43% this year. You can blame that on poor communication, says Fidelity's John Sweeney, but the changing economy may also be a culprit. Many workers now move from project to project as freelancers, or they work second or third jobs with unpredictable hours and pay — think Uber drivers. That gives them only a fuzzy idea of how much they'll make by the end of the year. Others are getting more of their salaries in bonuses. An end-of-the-year bonus is always welcome, but you can't count on it. Generation X couples are the worst at judging their partners' income, with 55% getting it wrong. This generation — in their late 30s and 40s, at or near the peak of their careers — is also the likeliest to get bonus pay, Sweeney notes. Younger millennials have simpler finances, and only 34% of them got the question wrong. Baby boomers, many of them winding down their careers as they approach retirement, got it wrong 42% of the time. There's nothing wrong with couples splitting up the work. One might handle the monthly checks, while the other cleans the bathroom. But it's worrying if spouses don't know what each other are spending, earning or even investing. According to Fidelity, 36% of couples also disagree on how many investable assets they have. Without a clear picture of their finances now, it can be impossible for couples to plan well for the future.