Dear Liz: I’ve been using a free credit site to learn more about credit reports and credit scores. Recently I looked around and found reviews about how “horribly inaccurate” these free scores are. Where can I go to find my real FICO credit scores? I need the ones that matter, the ones that lenders use.

Answer: Some free scores aren’t used by any lenders. But many sites these days give out VantageScores, a FICO rival that’s being used in a growing number of credit decisions. So VantageScores are “real” scores, just not the most commonly used scores.

Here’s the thing, though: You generally can’t predict which scores a lender will use. Not only are there different name brands, but FICO offers versions customized for certain types of lending. The scores typically used by credit card issuers are different from the ones used by auto lenders, for example. These industry-specific FICO scores are on a 250-to-900 scale, rather than the 300-to-850 scale used by other FICO scores.

There are also different generations of each type of score, much like the different operating systems for your computer. Some lenders quickly upgrade to the latest version, just as some computer users upgraded to Windows 10 when it came out. Others use older versions of the scores, just as users may cling to Vista or XP. (For you Mac users, that would be something like hanging on to Mountain Lion or Snow Leopard instead of updating to El Capitan.)

Mortgage lenders, in particular, use relatively old versions of FICO. That’s because the agencies that buy most home loans, Fannie Mae and Freddie Mac, haven’t updated their requirements so that lenders can use newer versions.

Some credit card companies offer their customers free FICO scores, typically from one bureau. You can get a glimpse of the array of scores lenders might use by buying the most commonly used FICO, the FICO 8, for about $20 each from MyFico.com. Along with each FICO 8 you buy (you can buy three, one from each of the three major credit bureaus), you’ll get additional versions used for auto, credit card and mortgage lending.

If you’re going to be in the market for a major loan, such as a car loan or a mortgage, it makes sense to buy your FICOs so you can get a better idea of how lenders might view you. If you’re just interested in tracking your scores generally, though, the free versions can be perfectly adequate.