When a woman hides spending from her husband, she's likely to conceal beauty purchases, such as cosmetics, an expensive purse, or a salon visit.
When men sneak around with money, they commonly spend on entertainment, guns, power tools, even cars.
And more of us do it than you might think.
According to a 2012 survey of 23,230 men and women by TODAY.com and SELF.com, almost half of all married adults admit to keeping money secrets.
Lying to a partner about money was admitted by 56 percent of women and 37 percent of men in the poll. Thirty-two percent of women said they have hidden purchases from their partner compared with 17 percent of men.
At the same time, honesty about money is a value many married men and women say they prize in relationships. Sixty-three percent of men and 70 percent of women said they think honesty about money is as important as remaining monogamous.
While seemingly trivial, hiding expenses can damage relationships and be a sign of deeper problems.
"Financial infidelity is marked by secrecy. Secrecy is a hallmark of the loss of intimacy," said John K. Bell, a therapist and licensed clinical social worker based in Louisville, Ky. "Financial infidelity can certainly damage a relationship beyond repair ... just like sexual infidelity."
Women, more than men, are likely to avoid conversations about money, said author and financial pundit Suze Orman. Many women assume that attitude because when it comes to money, "history favors the man, as handling the money was always the man's domain," Orman said in her 2007 book, "Women and Money."
"It is important that you have a totally open relationship about every penny you have and you do not have. I am asking you to settle for nothing less," she wrote. After bills are paid and savings goals are met each month, Orman wrote, couples should divide extra funds into two equal parts. The money can then be deposited in separate checking accounts for each partner to spend as each wishes.
Overtime at her nursing job helps Heather Lynn Kluemper, 40, stock a "secret slush fund" for quarterly, $250 wrinkle injections, facials and peels at the dermatologist. Kluemper said her husband, a banker, is unaware of her Botox bank account.
"It's non-negotiable. It's mine. I like that I can treat myself without having to ask permission," said Kluemper, who relocated from Louisville to Lansing, Mich., in 2009 for her husband's career. Her hidden "me fund" buoys her spirits amid the duties of being a wife of 16 years, a full-time nurse to brain-injured patients and mother of four boys, she said.
When Jackie Bay's first marriage ended, money was a big battle. Her former spouse made significant purchases just before he suddenly left the marriage in 2001, she said. The breakup left her with a mortgage and new second mortgage she could not afford.
Bay, 45, filed for bankruptcy protection as a result, she said. Her ex-husband confirmed he still owns the two-bedroom, one-bath cottage property but declined to comment further.
On Dec. 10, Bay celebrated her first anniversary with a second husband, a former construction worker who is a full-time student at ITT Technical Institute, where Bay works as an administrative assistant. He works odd jobs as a contractor.
Until he finds full-time employment upon graduation in June as a computer network specialist, Bay is paying their bills from her own bank account. If he uses her bank debit card for household expenses, they review receipts together. The husband's spending money comes from a joint account they both deposit funds into as needed.
"He has no money and no possessions. All he cares about is me. And we'll probably get along until he does start making money," Bay said.
Keeping track of joint accounts is easier than ever with the advent of electronic banking, Louisville divorce lawyer A. Holland Houston said. Engaged couples should even share credit scores, she added. The hard part, she said, is being willing to have candid conversations before tying the knot.
"If you are getting married and don't trust each other, why are you getting married?" Holland said. "People have to know what the other person is doing, because they could end up paying for it someday."
What is your money personality?
"Very few people feel neutral about money," said Louisville, Ky., therapist John K. Bell. "We each have clear values about how we view money and a couple must learn to be open and honest about those values and feelings."
Couples can more easily talk about money if they identify common, and often unconscious, financial attitudes:
"Money Avoidance" beliefs contend that money is bad and prompt some people to shy away from reviewing bills or statements. People with this attitude may have contempt for affluent people. These attitudes may sabotage financial success and promote compulsive shopping.
"Money Vigilance" behaviors include being "alert, watchful and concerned about financial welfare." People with these beliefs eschew credit, pay cash, are leery of risk and may withhold financial information from loved ones.
People with "Money Status" attitudes "see net worth and self-worth as being synonymous," believe "poor people are lazy," and will buy only new items. Compulsive spending can be a problem as they try to give the impression of wealth.
"Money Worship" attitudes include the belief that "money is power," and "if you have money, someone will take it away from you."