Keeping secrets usually has its roots in attitudes about money.
"It's 'my' money, and then all of a sudden you're in a relationship and it's 'our' money," said certified financial planner Doug Kinsey, a partner at Artifex Financial Group in Dayton, Ohio.
People can be tempted to withhold some information (and cash)—particularly about expenses that might be perceived as frivolous or embarrassing. Kinsey said he's seen several cases of people hiding money to spend on a hobby they thought their spouse wouldn't approve of.
Lack of communication is what makes deception possible, though, according to certified financial planner Lewis Altfest, CEO of Altfest Personal Wealth Management in New York. It's still common to see one partner take primary control of the finances, he said, which without communication leaves the other in the dark.
"Delegation is OK," Altfest said. "But knowing what's going on, taking an interest, is healthy."
(See chart below for the reasoning behind financial infidelity.)
Reasons aren't all selfish, either.
"It can be out of some misguided sense of protecting the other spouse," said certified financial planner William V. Suplee IV, president of Structured Asset Management in Paoli, Pa. He's said he has seen several instances in which husbands' avoided telling their wives about investment losses to keep them from worrying, and one in which a wife withdrew retirement funds to pay for college for the couple's child.
The cost of deception
Whether small or large scale, financial infidelity can be damaging both financially and romantically. Three-quarters of consumers experiencing it saw some relationship fallout, and 10 percent of them got divorced as a result, according to NEFE.
Sonya Britt, an assistant professor at Kansas State University's Institute of Personal Financial Planning, confirms that fighting about money is the top predictor for divorce.