Money expert Jean Chatzky: How to avoid the biggest end-of-year money mistake

Holiday expenses add up quickly — and they're easy to justify.

"We're celebrating, we're happy and this is a big New Year with the new decade," says Jean Chatzky, personal finance expert and co-founder of HerMoney. But the biggest end-of-year money mistake, she tells CNBC Make It, "is overdoing it during the holidays."

It's also a common mistake: Nearly half of Americans, 43%, admit that they're likely to overspend during the holidays, according to a survey from refurbished tech seller Decluttr. And 28% anticipate going into debt after holiday shopping.

To avoid overspending, Chatzky recommends starting by setting a reasonable budget. "Figure out what you can afford to spend on the holidays — and not just gifts for people, but the entertaining, the food and the transportation to and from parties," she says. "If you're Ubering to a party, you've got to count that as part of your holiday budget."

Review how much you spent last season, she adds: "Look back at your credit card statements. Where did your money go last Thanksgiving to New Years? How much more did you spend? What are you going to do this year to cut back a little bit?"

Once you establish your budget, stick to it. However, that's easier said than done. While over half of Americans, 53%, have a holiday budget, only one-fifth of those say they'll actually stick to it, a Yelp survey finds. Plus, "of those who don't stick to their budget, the average respondent will overspend by $489," the survey says.

Here are three strategies to help you stay on track this holiday season.

You can't stick to a budget if you don't know where your money is going. Record any holiday-related purchases in a notebook or spreadsheet to keep track of how much you've spent. The number may surprise you.

Tally up the total every few days so you know exactly how much "holiday money" you have left to spend.

Stores are carefully designed to trick you into overspending. For starters, they get you in the door with big, red "SALE" signs.

"Recognize what's a deal and what's not," says Chatzky. "If you're on the mailing list for a department store and they send you coupons for 20% or 30% off every time you turn around, then the holiday 'sale' that they're running for 30% off is not really a sale.

"Do your research online ahead of time to figure out if you're really saving money or if this is just the regularly scheduled price that's being called a 'deal.'"

Look out for other common tricks stores use as well, like placing pricier items at eye level and loading the checkout aisle with tempting products.

If you're up for a more extreme budgeting strategy, try going cash-only. That means you withdraw the amount you've allocated for holiday spending in hard cash and commit to using just that amount.

Once you've gone through your cash-only "holiday fund," you're done spending until the new year. To ensure you won't go over budget, leave your credit cards at home.

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