The financial secrets of American couples

Many American couples keep financial secrets from each other, including hiding bank or credit card accounts.

About 13 million people have hidden a bank or credit card account from their spouse, partner or significant other, according to a new survey from CreditCards.com. Spending is also an issue for many couples: The survey found that one in five Americans have spent more than $500 without telling their spouse.

Interestingly, the genders aren't alike when it comes to secretive spending. It turns out men are almost twice as likely to shell out $500 for a purchase without informing their partner, the study found. While having a hidden account isn't necessarily a red flag -- it could be used to save up for an engagement ring or a surprise vacation -- the research hints at the ways couples sometimes fail to communicate with each other about financial issues.

"The underlying theme in all of this is just that honesty and openness are important with any relationship, but it's really important when it comes to money," said Matt Schulz, a senior analyst at CreditCards.com. "If you hide some financial secrets, it's natural for the other person to ask, 'I wonder what else they are hiding?'"

It may be a surprise that financial secrets can add stress to a relationship. Arguments about money can be a predictor of divorce, according to a 2013 study about relationships from Kansas State University.

Many more Americans are fine about spending smaller amounts without their partners' knowledge, CreditCards.com found. About four out of 10 have spent more than $100 without informing their significant other, the survey said.

But they're not hypocritical. Almost one-quarter said they would be fine with their partner shelling out $500 without informing them. Almost half said they wouldn't blink if their partner spent $100 without telling them, the survey found.

"It's important for the folks to know what the boundaries are," Schulz said. "Depending on how much money you have, how comfortable you are with your partner, the boundaries can vary really widely from couple to couple."