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Of all the topics that can cause marital flashpoints, money is near the top. Forget sleeping with the window open or closed — the biggest fights are likelier to spring up when someone blows the budget or hidden debt comes to light. For more than half the couples surveyed by Fidelity in their report, Couples and Money, cash plays a significant part in the relationship — and when debt is on the table, the impact is far from positive. Of couples who are concerned about debt, 46 percent say money is the biggest relationship challenge. To compare, just 16 percent of couples who aren’t burdened with debt say money is a challenge.

Retirement planning is another wellspring of disagreement. It may be decades away or it may be looming on the horizon. But many couples in Fidelity’s survey simply cannot agree on what age both think is ideal for retirement or how much they’ll need to save to pay for their current way of life. Nearly half (49 percent in the study) said they have "no idea.” “Anecdotally, I’ve heard these same kinds of things from couples,” says Judy Ward, senior financial planner and vice president at T. Rowe Price. “We may have a vision of retirement yet neglect to see if our spouse is on the same page.” The solution to retirement squabbles is to improve communication. Ward says couples can write out their vision of retirement separately, then compare notes. If one person pictures a lake in Canada and the other is dreaming of a Miami condo, “clearly you’ll have some compromising to do,” she says.

The art of communication

The study revealed other misunderstandings and gaps in knowledge between spouses, even though most couples claim to communicate either exceptionally or very well. Communication misfires run the gamut from simple disagreements to deeper structural problems. It might seem like an easy question to answer, but one in five couples couldn't agree how long they’ve been together. One in seven couples couldn’t accurately report their other half’s employment status. Over the years some financial concerns have shifted. Building up an emergency savings account was a bigger concern for 50 percent of couples in 2013. Two years later this percentage had dipped slightly, to 43 percent. This year, just 38 percent of couples expressed concern over emergency savings.