Approximately 7.2 million Americans – including 4.4 million men and 2.8 million women – have hidden a bank or credit card account from their live-in spouse or partner, according to a new CreditCards.com report. But that's not the only financial secret people are keeping.

One in five Americans have spent $500 or more on a purchase without their partner's knowledge, with men much more likely to have done so. 26% of men have spent more than $500 without notifying their significant other versus just 14% of women. The biggest secret spenders have annual household incomes between $50,000 and $74,999 and are between the ages of 18 and 29.

Perhaps surprisingly, many Americans say they are fine with their spouse or significant other making big purchases without telling them. Nearly 1 in 3 men (31%) are okay with their spouse or partner spending more than $500 without their knowledge versus only 18% of women.

"These secrets are a recipe for disaster," says Matt Schulz, CreditCards.com's senior industry analyst. "If you and your significant other aren't honest with each other about what you're spending, you never really know how much money you have and that can lead to big problems."

For example, secret spending can make it impossible to make an accurate household budget. It can also lead to increased credit card debt, not to mention added stress on your relationship.

Still, not all Americans are comfortable with these secret spending sprees. Approximately one-third of Americans (31%) don't think their spouse or partner should be able to spend more than $100 without telling them. That includes 37% of women, but just 23% of men.