Car insurance, for the most part, is a very confusing expense. Quotes for identical coverages can vary by several hundred dollars from provider to provider, which leads us to this question: exactly how are insurance companies determining their premiums? Is there a set of proprietary formulas that providers use to calculate how much they should charge their customers?

Consumer Reports decided to find out. In a wide-ranging study analyzing over two billion car insurance price quotes from over 700 companies in all 50 states, Consumer Reports created a sample driver–clean record, great credit, owns a sensible Toyota Camry–to generate some baseline numbers, then varied that driver’s specifications to figure out which factors most affected their insurance cost. If the sample driver then got in one accident, for instance, how much would his premium increase?

The results were fascinating. What Consumer Reports discovered is that while a recent car accident would raise premium costs (which is to be expected), the biggest price bump occurred when credit score is factored into the insurance pricing calculus. Yes, you read that right: car insurance companies are using your credit score to figure out just how risky you are to insure. Consumer Reports concluded that the lower or “worse” your credit score, the more likely insurance companies think you are to file a claim. So they price accordingly, adding an average of $1301 to the annual premium of drivers with what they consider poor credit.

Based on their data, Consumer Reports figured out that insurance companies are using their own version of a FICO score, “cherry-picking about 30 of almost 130 elements in a credit report” to put together a number that “has more of an impact on your premium price than any other factor.” And since insurance providers are not required by law to disclose how they arrived at your quote, consumers pay the price–quite literally–for their lack of transparency. Currently, only California, Hawaii, and Massachusetts prohibit car insurance companies from figuring credit scores into their prices.

So as a consumer, what can you do about these practices (besides moving to a state that outlaws them)? Consumer Reports has started a petition asking all 50 State Insurance Commissioners to “price me by how I drive, not by who you think I am!” (To sign, click here, then scroll down.) We also recommend shopping through a car insurance broker, who can compare several different companies at once to offer you the best combination of pricing and terms and conditions, since they are not beholden to one provider. We encourage you to follow DWKMRS’s blog for more updates on car insurance pricing and Florida law.

Want to learn more? Visit our free resources page for more educational content on consumer and victims’ rights.