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Kai Ryssdal: Want to buy a house someday? Finance a car? Great. Good for you. Hope you've got good credit.

While you might think you do, chances are you don't know exactly how good or bad your credit score really is. But knowing's gonna get a little easier thanks to one of the biggest class action lawsuits ever. 160 million Americans will be able to monitor one credit score free of charge.

Our New York bureau chief Jill Barshay explains.

[Clip from Credit Score Ad]: The higher my credit score, the better chance I have of saving a lot of money. Do you know your credit score?

Jill Barshay: Up to now, credit reporting agencies charged you $10 or more a month for that information. Now, TransUnion will let anyone who's taken out a credit card or a loan since 1987 monitor his credit score for six months at no charge.

But the figure consumers will get from TransUnion isn't the same as a FICO score -- that's the gauge of credit that lenders use. If you want the FICO score, you'll have to pay extra.

Ken McEldowney is the executive director of Consumer Action, an advocacy group. He says TransUnion sold Americans' private credit information. He says the real value of this settlement is to deter other companies from doing the same.

Ken McEldowney: I think one of the things it's going to do is it should do a wake up call for not just credit reporting agencies, but also for other corporations who may have been taking privacy concerns a little too lightly.

TransUnion will tell users when their score goes up and down. Liz Pulliam Weston writes about personal finance. She says consumers could learn a lot about their credit if they subscribe.

Liz Pulliam Weston: If you, for example, go out, put your whole vacation on your credit card, max out your card, you're going to watch your credit score plummet, and that's good for people to know, because your score is very sensitive to how much of your credit you're using.

Pulliam says says most people don't need to monitor their credit monthly unless they've been a victim of identity theft.

I'm Jill Barshay for Marketplace.