Millions of Americans keeping financial secrets from spouses

Roughly 1 in 5 Americans in a live-in relationship keeps a checking, savings or credit card account hidden from their spouse or partner. That adds up to 29 million people whose financial secrets could plague their love lives, according to a CreditCards.com report.

Secret accounts are most common among millennials, 28 percent of whom are currently hiding bank or credit cards from their live-in partners, the study shows.

More than half of the people surveyed likened keeping financial secrets to physical infidelity, qualifying it as at least equal in severity to physical cheating.

"I think it's very damaging from a trust standpoint and also from a dollars and cents standpoint," said CreditCard.com industry analyst Ted Rossman. "If a secret account includes credit card debt, that's a meaningful chunk out of the household budget."

Be upfront about separate spending, "freedom funds"

Rossman added there's nothing wrong with couples keeping their finances separate, but it's important to be upfront about it. "Communication about money is so important in a relationship," he explained. "It's hard enough to reach big financial goals when you're on the same page. It's really almost impossible when you're not on the same page."

In the best-case scenario, someone might keep a pool of money secret in order to surprise their spouse with a vacation, or anniversary present. On the other end of the spectrum, a husband or wife could be using the secret account to finance an affair. "Someone would have a credit card they use to go to hotels, travel, and buy them gifts," Rosman said.

So-called "freedom funds" are common, too, among people who aren't sure their relationships will last. "They will say, "This is mine if this relationship doesn't work out, that's what I will take to try to start over,' " Rossman said.

Digital banking tools vs. the dangers of household mail

San Francisco financial planner Sarah Behr says financial deception is symptomatic of deeper fissures in a relationship.

"You don't feel like your goals are aligned and either one or both people don't necessarily feel like they can be candid," she said. "Being secretive about debt or other issues gets at the core of trust in the same way infidelity can when you find out that someone has been spending a lot without telling you, or created some mess you are both on the hook for."

She said her first marriage crumbled after her then-husband repeatedly misspent funds — on mountain bikes and fly fishing equipment -- that the couple agreed they would not put towards recreation and leisure. "I lost trust in his ability to spend wisely," she said.

Digital banking tools have made it increasingly easy to hide this kind of spending. One thing to watch out for, though, is a partner who intercepts household mail.

"Some things are required by law to go snail mail so you would have to get to the mailbox and make sure you cut it off and then suppress everything to paperless billing," Behr said.

Credit checks before wedding bells ring

Other financial advisers suggest credit and background checks of your romantic partner before tying the knot.

"If you are married you would be liable for anything the other person has, including tax debt, credit card debt and student loans," said New York City financial planner Brian Walls. "They could rack up credit card debt without the other one knowing. They could do some damage."

There's no right or wrong way for a couple to manage their finances, but secrecy is corrosive and damaging when it comes to money.

"If someone finds out about their partner's account when they are trusting they are on the same page, it would create a really big rift in that trust going forward if someone is doing stuff behind their back," said Dallas certified financial planner Katie Brewer.

"The best way for a couple to manage their finance is whatever way allows them to stay married," she added.