I am 26 years old and a recent college graduate. I have good credit, and I work full time. I am thinking about adding a credit card that gives cash back for using it. I currently have two open in good standing — one that I have had since I was 18, the other since I was 19. I am able to pay each one completely each month, but only one of them has a rewards program. Would it be beneficial for me to obtain a third card with a cash back program, or stay with the two that I have? – Michael, Rancho Cucamonga, Calif.

From a credit perspective, adding an additional card will eventually be good for your credit score, as long as you aren't carrying a balance on it, says John Ulzheimer, president of consumer education at SmartCredit.com. That's because your available credit will be higher, so if you're still charging the same amount, your credit utilization ratio will be lower, which leads to a higher score. Though applying for a new card will ding your score in the short term, using that plastic responsibly will benefit your score over time, confirms Tom Quinn of Credit.com.

So, for instance, if your current cards offer a combined total of $10,000 in available credit, and you charge $1,000 a month, your credit utilization ratio is about 10%. If you add another $5,000 of available credit with a new card, but charge the same amount, your credit utilization ratio drops to 6.7%. (And your credit score should rise accordingly.)

But a reward card is only beneficial if you read the fine print and use it responsibly, says Jay Hutchins, a financial planner in Lebanon, N.H. "Cash back arrangements can be beneficial to cardholders who dutifully pay their full balance every quarter," Hutchins says. "But the rules vary among cards and can be both tedious and confusing."

For instance, many cards offer a teaser cash-back rate for a few introductory months, then drop it after that. Others pay varying cash back rates based on the type of purchase (groceries or drugstore items, say), or whether the purchase was made through the card's online portal. Compare the cash-back card's rewards with your own spending patterns to make sure you get the best one for you.

Make sure, also, that the reward component doesn't prompt you to fritter your money away. Cash-back cards can encourage people to spend more and pile up more debt, according to a 2010 study by the Federal Reserve Bank of Chicago. Spending an extra $200 a month to achieve $2 in rewards doesn't make monetary sense.

And last, whatever you do, don't carry a balance on the card, since reward credit cards tend to have higher interest rates than other cards. Just one month's interest fees could wipe out your cash back rewards for the year.

— Kate Ashford

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