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By Meredith Clark

Financial infidelity in relationships is a serious transgression: It erodes trust, increases tension and is deeply unsexy. Study after study has found that money and sex are two of the main reasons relationships fail, and that communication about each person's financial problems, needs and fears — or even just their lack of money — is the way to defuse conflicts.

People know this: A recently released report from CreditCards.com found that 31 percent of respondents consider “financial infidelity” to be worse than cheating romantically and almost half also wonder whether their partners are totally honest about money.

And yet, some 15 million American adults in live-in relationships have a bank account or credit card that they are concealing from their partners, and another nine million admitted that they once had some form of secret account. Generational breakdowns in the CreditCards.com data aren't hopeful: Almost a third of millennials surveyed admitted to keeping financial secrets, while only eight percent of people older than 73 said they had deceived their partners.

To these people, one can only say: What are you doing?

Now that most women and men come to relationships on a more even economic footing, it’s easier to see financial infidelity as a serious betrayal.

You can’t have a healthy relationship without honesty; every self-help book, TV lifestyle guru, and romantic comedy will say so. Romantic monogamy has been the standard expectation for relationships for centuries but, for most of that time, money wasn’t something that warranted discussion. Men had sole control over household income and bank accounts anyway; married women in the U.S. couldn’t even apply for their own credit cards until 1974, for example. But now that most women and men come to relationships on a more even economic footing, it’s easier to see financial infidelity as a serious betrayal. When a loved one hides how they spend and what they’re spending on, it’s proof of a lack of trust or respect that cuts just as deeply as physical cheating.

There's also a gendered aspect: Of the 11 percent of this survey’s respondents who said they avoid the topic, women were far more likely to admit to this than men. This attitude is dangerous: Women earn less than men on average, they’re still the most likely parent to leave work to raise children, they live longer than men and they’re more likely to live in poverty than men. Divorce hits women harder than men, and it used to be a recipe for destitution. Even today, thought, women who work can expect a 20 percent decline in income after divorce, while men are likely to see a 30 percent increase.

It may be awkward or painful, but it’s better to know the full extent of a relationship’s financial situation, for both parties.

One demoralizing reason why so many couples struggle to talk openly about money is probably that Americans in general have terrible financial literacy.

One demoralizing reason why so many couples struggle to talk openly about money is probably that Americans in general have terrible financial literacy. Nearly two-thirds of Americans couldn’t pass a basic test in 2015, and that number has been increasing since the 2008 financial crisis. It’s well known that American students have fallen behind their global peers in STEM, but that means they struggle with simple ideas like calculating interest, making a budget and assessing risk. Only 17 states require some kind of financial education class for high school students. That leaves a lot of young people without a sense of what they don’t know, which means learning through potentially credit-ruining mistakes.

But it’s too easy to use these numbers as another excuse to heap scorn on couples that are drowning in student debt or struggling to find a job that has health insurance. Economic inequality in the U.S. has been increasing for decades, and there are pockets of poverty so severe that the United Nations launched a human rights investigation. Almost everyone who is not fabulously wealthy will deal with financial challenges at some point, and talking openly and without shame about debts and expenses can help couples separate “good” debt from “bad debt” and make a plan.

That can be done without a ton of money: It could be as simple as looking through credit cards to compare interest rates and doing a balance transfer to a card with a better one, checking on what company is in charge of a student loan, or switching to a bank or credit union that doesn’t charge fees for maintaining a minimum balance. Small, thoughtful actions are essential to keeping a relationship healthy, and that applies as much to lugging a bag of change to a CoinStar as it does to buying flowers.

It’s as crucial for couples to figure out whether they share the same financial values as it is to make sure they share the same sexual habits.

Luckily, almost two-thirds of people surveyed said they talk about money at least a few times a month, which means most Americans are aware of how important those conversations are, even if they aren’t being completely up front about what’s happening in their bank accounts. And for those who aren't, it’s a problem that can be solved relatively easily compared to other economic issues. Take the time to talk through finances with a partner — goals, past mistakes and the current situation — and do it before things get too serious. Better to walk away from a relationship because someone has $20,000 in credit card debt than find yourself saddled with his or her massive monthly payments down the line (especially if they never end the spending habits that caused their problems in the first place).

If there’s anything surprising about the CreditCards.com survey, it’s that only 31 percent of people think financial infidelity is a serious transgression. It’s as crucial for couples to figure out whether they share the same financial values as it is to make sure they share the same sexual habits. Avoiding conversations about how we think of and spend money can breed resentment in a partner who earns less, lead people to stay in relationships that are unhealthy because they have no safety net and endanger people's long-term financial security. Dishonesty about money can lead to problems that last decades longer than a broken heart.

Meredith Clark is a freelance writer and editor in New York City.