NEW YORK (CBSNewYork) — Whether you’re doing your holiday shopping in stores or online, consumer experts stress caution.

For many Americans, those holiday deals add up to a mountain of debt come January.

“They don’t plan,” Eric Stuerken, a consumer credit expert and co-founder of Better Qualified, told CBS2’s Jessica Layton.

He said his office is always buzzing with clients after Christmas.

“One of the biggest mistakes is they don’t buy on cash. They’re going into their credit lines or their credit cards,” he said. “Thirty percent of our credit score is based on what we use. It’s called utilization. So if you’re using more than you’re used to and you max out your card near 100 percent, your score is going down 30 percent.”

Read: Black Friday Shoppers Hit The Stores In Search Of Holiday Deals

Stuerken said in most cases, cash is king. It keeps people within their financial means.

What about those store credit cards that offer big percentages off when you open them? He says that depends on how good you are at paying off your purchases.

“In the end of the day, you’ll probably have an interest rate somewhere in the high 20s. And if you can’t pay it off and you’re making the minimum payment, that purchase you thought you were saving 50 percent on – it goes back to what you purchased and sometimes even more,” said Stuerken.

Beware of your personal shopping habits. Starting too early may mean you spend too much over the next month. Start too late, and you could splurge on something unnecessary.

Just as Santa Claus makes a list, you should write down exactly what you can afford and stick to it.

“The numbers sink in and you’re not waking up in January to a reaction where it’s, ‘Oh my god, I did this,’ and now the rest of your month is a panic mode of how you’re going to start to pay this stuff,” Stuerken said.

Bottom line: being generous does not mean over-spending.

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