And Ramsey says it's not sound financial practice.
"When you're lying about your money, whether it's spending, debt or saving, when it's a secret from your spouse, that's financial infidelity," Ramsey says. "I don't mind anyone having savings, but I mind people hiding it.
"Anytime you have deception in a relationship, whether it's with a spouse or a boss, you're a liar. It breaks the relationship down.
"Unless your spouse has some type of actual disorder, like they are a compulsive gambler, there is no reason to ever hide money or debt from your spouse. It never works out for the best.
"It's OK to have some squirrel money. That's what we call it. My wife squirrels money away, but I know it's there. We call it the decorating fund, because that's what she's going to spend it on."
Ramsey adds, "Unfortunately, I see financial infidelity all the time. Sometimes they say they hide money because they're afraid their spouse will spend it. Sometimes they're afraid their spouse won't give them money when they want it. Sometimes they're afraid to talk to their spouse about money."
What can couples do to come together in this regard?
Among Ramsey's suggestions:
To come up with a clothing budget, for instance, agree on a set amount for clothing to put in an envelope. You can't spend it on anything but clothing, but you can spend it guilt-free and shame-free.