Most people have secrets from their significant other. Maybe you didn't really have the salad for dinner or perhaps one drink at the bar was actually four (or more).

For whatever reason, a lot of folks in committed relationships aren't fully honest with their partner. In many cases, that's innocuous enough, an extra cookie or the fact that the jeans you bought weren't actually on sale fall into white lie territory.

Some lies, however, are worse than others. Concealing bank accounts or credit cards, falls into that category for about a third of Americans in a committed relationship, according to a new report from CreditCards.com. Those folks, 31% of the total, believe that hiding accounts is worse than cheating physically.

A man and a woman look at piece of paper.

About one-third of people in live-in relationships consider secret financial accounts as bad as physical cheating. Image source: Getty Images.

How big is the problem?

Hiding bank and credit card accounts from a partner or spouse is more common than you might expect. Of the U.S. adults involved in a live-in romantic relationship, 15 million people currently have a credit card, checking account, or savings account that their partner or spouse doesn't know about. In addition, another nine million admit they used to have such an account, but say they have gotten rid of it.

About one-in-five U.S. adults in a live-in relationship (21%) either are guilty or have been guilty in the past of this behavior. This behavior does skew with (31%) of Millennials (18-37) having at some point kept an account secret from their current spouse or partner. The numbers decrease as ages go up with 24% of Generation X (38-53), 17% of Baby Boomers (54-72), and 8% of the Silent Generation (73+) admitting to this financial trickery.

How big a deal is this?

As noted above, 31% of those in a relationship consider that having a secret credit card, checking account or savings account is worse than cheating physically. That percentage increases for survey respondents in lower income brackets. 

The problem may at least partly be due to lack of communication. Only 63% of romantic partners discuss their finances at least a few times a month. That leaves a pretty big number that does not.

"Keeping financial secrets in a relationship, just like any other type of infidelity, is a sure-fire way to spark an argument," said CreditCards.com senior industry analyst Matt Schulz in a press release. "Honest ongoing communication about money is vital to any serious relationship. When in doubt, talk it out."

What should you do?

When it comes to relationships honesty is generally the best policy. In the case of finances, if you feel the need to keep secrets that may speak to a bigger problem in the relationship.

People who live together need to create a financial reality that both people operate under. That means being open about finances and being able to reach an agreement. If you can't, then perhaps being a live-in couple is not the correct move for you.

The Motley Fool has a disclosure policy.