A man seducing a woman(Photo: Courtesy of Prevention)

Admit it, ladies. You're having an affair. You know the type: He can put out all night if you push the right buttons -- for your PIN code, that is.

If you and your joint bank account are getting a little naughty on the side, you're not alone. A new study from Self magazine and Today.com surveyed 23,000 adults and found that almost half of spouses lie to each other about their finances.

And most of the cheaters -- 56% -- are women.

More from Prevention: 7 Mistakes Even Smart Couples Make

Go ahead and blame it on shopping. Women went to extremes to hide their habit (a whole third of them admitted to stashing purchases or receipts out of sight) and more than 25% said they pretended something was old when in fact it was fresh off the rack -- and we're not talking the sale rack, either.
We all know that honest communication is one of the keys to everlasting relationship bliss, but does the same necessarily apply to finances? Here are three times it's okay to be less than truthful about matters of the wallet, and three times to fess up:

Spend away when...

1. He deserves it Sometimes, you just can't accomplish a mission without a little stealth. A surprise birthday party for your loved one is the perfect opportunity to blow some secret cash (hey, somebody's got to pay the magician!), as long as you actually have the money, says Eleanor Blayney, consumer advocate and women's finance expert for the Certified Financial Planner Board of Standards. Make a gift or vacation category in your budget, or simply save up to make sure surprise can fit in your budget.

2. You have "mad money" Add a budget category for both of you called "mad money" -- dough that can be blown any which way, suggests Blayney. It's a great way to get those weekly manis or expensive boots without having to explain your purchasing choices.

3. You have separate accounts Having separate -- but not secret! -- bank accounts can actually boost relationships, says Blayney. By gaining financial autonomy, you're not beholden to your partner for how you use your money -- and vice versa.

More from Prevention: Secrets Of A Happy Relationship

You need to come clean when...

1. You don't have a budget Fortunately, the prehistoric days of wives having to ask for a household allowance are behind us, says Blayney. But if you have agreed-upon budget guidelines, it's not fair to anyone to lie about breaking them.

2. You have a secret account Not all financial sins are created equal. When it comes to keeping a secret credit card or account -- even if you're doing so to keep the peace by avoiding money arguments -- you're in troubled water. "Peaceful has huge potential to be very disruptive," she says. Come up with a more flexible budget instead.

3. You have a problem Shopping addictions -- when your spending becomes compulsive -- devastate families. Talking to your partner is one step, but you also need to seek outside help, says Blayney. Your best bet is to consult a therapist of credit counselor for advice.