It’s natural to fret about your credit score. Most Americans would do almost anything to improve it. Mistakes, of course, are bound to happen.

More than one in five credit card users have carried a balance to help improve their credit scores, according to a study released Monday by But carrying a balance is not one of the factors that comprises a credit score—and doing so could lead to more harm than good.

Leaving a balance past a payment due date causes cardholders to pay unnecessary interest, and could even negatively affect their credit score if the balance pushes their credit utilization too high.

Twenty-eight percent of millennials with a credit card said they have made this mistake, while only 25 percent of Gen-Xers and 16 percent of those age 54 and older admit to the same blunder.

The survey was conducted for the online marketplace by market-research firm GfK, which gathered data last month from 1,000 Americans aged 18 and older.

“The fact of the matter is that carrying a balance will never improve your credit,” said senior industry analyst Matt Schulz. “With interest rates at an all-time high, cardholders should aim to pay off their bills in full every month, and, more importantly, pay on time.”

Lower earners and those without a college education are also likely to fall victim to the misconception. Thirty percent of credit card users making under $50 thousand dollars per year have tried to improve their credit scores by carrying a balance, compared to 19 percent of those who earn over that amount. And 27 percent of cardholders without a college degree have done the same, compared to only 12 percent with a college education.

Many Americans are simply struggling to pay their credit card bills on time. Forty-two percent admit to paying a credit card bill late. And, once again, millennials tend to be the most habitual late-payers, with 10 percent reporting they have paid a late fee five or more times.

More than half of millennials said they paid a bill late because they did not have enough money at the time.

This article was provided by Bloomberg News.