When is free really not free? When it comes to getting your “free” credit report.

If you’re not careful, it could wind up costing you.

Plenty of TV, radio and Internet ads promise consumers a copy of their free credit report, but what they really want is to entice you into signing up for “credit monitoring” or other services. And those are decidedly not free, running anywhere from $15 to $30 a month or more on your credit card bill.

Sacramento, Calif., retiree Jim Fossum found out the hard way. In May, he thought he was going online to ask for a free copy of his credit report from AnnualCreditReport.com — the official website for such requests. He got the report with no problem, but was startled when a $29.95 monthly charge popped up on his next credit card bill.

“I got sucked into something I didn’t want,” said Fossum, 82, who isn’t sure how he wound up on a different site, GoldenScoresLLC.com, which started charging him for monthly credit monitoring.

“I found out that if you did not send a letter (opting out) within 10 days, you were automatically subscribed.”

Fossum’s experience is not uncommon. And that’s despite federal regulations that now require sites offering free credit reports to provide full disclosure about trial memberships and a link to the federally authorized AnnualCreditReport.com.

It also comes after a much-publicized Federal Trade Commission case in 2005 against FreeCreditReport.com, whose popular TV and radio ads featured a guitar-playing band with a catchy jingle. Accused of using deceptive tactics, FreeCreditReport was fined more than $1.2 million by the FTC.

“It’s unfair and deceptive to promise consumers something for free and then trick them into paying for products they didn’t want in the first place,” the FTC said in August 2005.

There’s only one website that is federally authorized to provide consumers with free annual credit reports: AnnualCreditReport.com. By law, everyone is entitled to a free credit report once a year from each of the three credit reporting bureaus: Equifax, Experian and TransUnion.

You can order them all at once. Some credit experts recommend spacing them out over a year, ordering one from a different bureau every four months, in order to have a continuous snapshot of your credit history.

In addition to the official AnnualCreditReport site, several companies will give you a free credit report and an estimated credit score — with no strings attached. They include: Bankrate.com, Credit.com, CreditKarma.com and CreditSesame.com.

The scores you receive are not the same as a FICO score, but these score estimates are based on the same credit history factors that go into a FICO score, said John Ulzheimer, consumer education president at SmartCredit.com.

“These free score estimates consider the same factors. It’s pretty darn close to what you’d get from FICO,” Ulzheimer said.

On its website, the FTC warns of “impostor” websites that are not part of the AnnualCreditReport.com program.

According to the FTC, some sites use terms like “free report” in their names. Others have URLs that purposely misspell “AnnualCreditReport.com,” hoping that you will mistakenly type in their name.

In some cases, the “free” product requires that you provide a credit card number, which is used to enroll you in a trial membership for various credit monitoring services. If you don’t cancel during the trial period, you could be agreeing to let the company charge fees to your credit card.

That’s apparently what happened with Fossum. It took several persistent phone calls to the Tennessee company before he was able to get the monthly credit-monitoring service canceled.

On his first call, Fossum said, the salesperson tried to up-sell him on other services that he didn’t need or want. He asked to speak with a supervisor but, after 20 minutes on hold, hung up. Only after calling back and “not being nice” was he able to get the service canceled.

Even so, the 82-year-old intends to scrutinize his credit card bills to be sure the charge doesn’t show up on future statements.

A call to GoldenScoresLLC was answered by a customer service manager, who declined to comment.