Is your spouse hiding money from you? New study says it’s likely.

Research has found that millions of Americans keep secret funds and make purchases behind their partners’ backs.

Money talks, and in more ways than one.

More than 7 million Americans have hidden a bank account or credit card from their spouse or partner, a new CreditCards.com study has found, and one in five have spent $500 or more on a purchase in secret. Men are also more likely than women to keep their personal funds hush-hush, according to the study.

The researchers call it “financial infidelity.”

"This is a big deal both in terms of your finances and in terms of your relationship," Matt Schulz, senior industry analyst for CreditCards.com, told CNBC. "Anytime you have this sort of secret being hidden, it naturally begs the question of what else is being hidden."

The study, released Wednesday, provides fuel for the hot-button issue of how couples should handle their finances. The consensus among experts seems to be that it’s different for everyone – but that lying or omitting financial facts is never OK.

“Money secrets have no place in a marriage,” money coach Kelley Long wrote for The Wall Street Journal.

Indeed, fighting about money is a top predictor of divorce, according to a 2013 Kansas State University study. Couples who argued about money tended to fight longer and use harsher words, the study found, and financial arguments were equally destructive regardless of how much each spouse earned.

So what’s the solution?

For some, the answer is in separate bank accounts.

“This gives each partner a sense of autonomy and financial independence, potentially saving them from endless hours of petty money fights,” Ms. Long wrote.

For others, the solution to money issues is in just the opposite: Sharing bank accounts, and thus building trust together. About 66 percent of American married couples still have joint bank accounts, according to a 2012 American Express survey. For Club Thrifty founder Holly Johnson, that’s just how it should be.

“Holding their assets and liabilities together serves to bind a couple to their common goals, forcing them to look beyond their personal wants and needs to see what is best for their family, their ‘team,’” she argued in a Wall Street Journal essay.

What it comes down to is going to sound familiar to anyone who has ever read a relationship book, blog, or article: “Communication is key,” Long wrote.  

That’s easier said than done – more than 40 percent of Americans find it harder to talk about money than about death, politics, or religion, according to a recent Wells Fargo survey. In some cases, a couple might need to set a monthly “financial date night,” or hire someone to serve as a neutral third party. But however the subject is breached, one thing is for sure: Staying silent on money matters is not an option.

"If you're keeping these sort of secrets you're making things harder on yourself and setting yourself up for trouble," CreditCards.com’s Mr. Schulz said. “Honesty is hard to beat.”