Even high earners can find themselves under a mountain of credit card debt if they let their spending go unchecked.

Jason, 40, and Megan, 34, earn a combined $256,000 a year and have around $3 million in assets, including their home, a second property and around $900,000 in investments. Yet they also owe $40,000 in credit card debt, they told self-made millionaire and money expert Ramit Sethi on a recent episode of his "Money for Couples" podcast. Their last names were not used.

The couple's high income and available assets are keeping them from being in a tough financial situation. But they also have a baby on the way, which will bring their costs up and lower their income as Megan takes time off. 

They could feasibly tap their savings and investments to wipe out their credit card debt almost immediately. But without addressing how the debt got there, they could wind up repeating the same mistakes, their conversation with Sethi showed.

When asked how they racked up so much debt, the couple mentioned emergencies like a flood, a car accident and other unexpected costs. In turn, they maxed out their cards. But to Sethi, "that's just sloppy financial management."

"A couple making $256,000 a year should not have the issue of 'there's no room on a card,'" he said.

Here's how Sethi recommended they proceed.

'Don't leave it up to romance'

To get their spending in check, Sethi recommended Jason and Megan operate their home finances more like a business, advice he's given other couples on his show as well. When it comes to decisions like which partner is doing the grocery shopping and whether they can afford a vacation, the couple should have standard operating procedures in place.

"You've got to have a really defined set of rules," Sethi said. "It would be like a McDonald's franchise."

But first, they may need to rethink how they make financial decisions. Megan has been in charge of things like groceries and home upkeep, but Jason has been in control of all the financial accounts and decision-making. That means she still has to check with Jason or ask to take one of his cards to use at the store.

Jason wasn't necessarily strict with Megan's spending, but it still created an unfair dynamic in their relationship, Sethi said.

"In my opinion, the way they're talking about their accounts…is going to set them up very poorly going forward," Sethi said. "Who wants to have to ask their partner for an allowance, and who wants to have that conversation 300 times a month for groceries and diapers and a car and Starbucks?"

The couple also has quite different attitudes about money. Jason is obsessive about optimizing his finances, while and Megan tends to avoid the topic, making it difficult to get on the same page.

"In my mind, I just think it's always going to work out," Megan said. "I don't feel like I'm ever going to be homeless, car-less or in any dire strait situation."

Ultimately, Sethi encouraged the couple to fully combine their finances to simplify their budget and long-term planning, and to decide what they want their joint financial goals to be.

Then, they can institute a standard operating procedure with rules, such as putting cash windfalls toward their credit card debt or discussing purchases over a certain price. These can help de-stress financial decisions and bring a more equal dynamic to their household.

"Write [your SOP] down. Don't leave it up to romance and certainly not like, 'Oh, let's talk about it,'" Sethi said. "Because the last thing you want to do is be like, 'Babe, can you give me money for Formula 409?'"

Check out the full episode here.

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