If you're trying to recover from a bad credit history, or just trying to boost your credit score before applying for a mortgage, becoming an authorized user on someone's credit card account might really help your cause. What is an authorized user? It's someone who gets all the upside of the credit card (access to credit) with none of the downside (responsibility for payments). But the best part of being an authorized user may be the fact that the cardholder's payment history also populates your own credit report. If your Mom-in-shining armor agrees to help you out, you benefit from her payment history. Better yet if she puts you on an account that she has had since the Reagan administration -- longevity of your credit history is one factor in scoring.

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Don't be stupid.

Know yourself. If you have a thing for Ambien-fueled Ebay binges at 3 AM, do NOT use the card. Don't even get one in your name. Tell your helper that you don't even want to know the name of the issuer! Or you might stick your would-be savior with a big bill, over-limit fees, a default interest rate, and tank down both of your credit scores.

Can the authorized user thing bite you in the butt?

Obviously this presents a risk to Mom, the authorizor, but how about you, the authorizee? It can get you in a couple of ways. First, if Mom chooses the wrong account to put you on you might not benefit. Some card companies like MBNA only report the history of authorized users to credit bureaus if they are spouses of the responsible party.

Second, what if Mom goes off the deep end and misses a few payments on that account? Yes, it shows up on your account and could torpedo your credit score. Oops.

Third, it's not just your payment history that matters. Suppose you have a buddy who makes you an authorized user on a card with a $3,000 limit. He has other cards and a total credit limit of $30,000. But he likes the $3,000 card and uses it a lot. If that sucker is maxed out, his utilization ratio is 10%. No biggie. However, you only have the $3,000 card on your report (because you have bad credit and no one will give you a credit card of your own, duh). When that $3,000 card is maxed out, your credit utilization is 100%, ew. Think that doesn't matter too much? You would be wrong -- credit utilization is 30% of your FICO credit score, only slightly less important than payment history.

One last butt bite...

Finally, you may not get as big a kick from piggybacking on your pal's Amex. Fair, Isaac, the company that created FICO, has stated that its new algorithms control for piggybackers who are not "legit" and so you would not benefit as much as you would have in the past. But of course they won't get more specific because then they'd have to kill you.....