Your FICO score, a.k.a. your credit score, makes a big difference in how lenders see you—and what they’ll charge you. But what, exactly, goes into calculating that all-important score? Here is a quick explanation.

-35 percent of your FICO score is based on your payment history. This is a large chunk of your score, so you want to make sure you always pay all of your bills on time.

-30 percent of your FICO score is based on capacity, or the amount owed revolving debt. This can make a difference as well, so don’t max out your cards and try to owe no more than 30 percent of your available credit at any given time.

-15 percent of your FICO score is based on length of your credit history. This includes the length of new credit and total credit history. This one is why it’s usually best to keep old accounts open, even if you no longer use them frequently.

-10 percent of your FICO score is based on your mix of credit. This is your percent of revolving credit (credit cards), installment loans (student and car loans) and mortgage loans. You want to have a good mix of all three types of credit to get the best score.

-10 percent of your FICO score is based on accumulation, or new credit and inquiries. Don’t apply for lots of credit at once—too many inquiries may indicate that you are overextending yourself financially.

Don’t worry if your credit score is not exactly where you want it to be—the major drawback to credit scoring is that it relies on information in your credit report, which is likely to contain errors. That is why it is critical that you check your credit reports annually, or at the very least three to six months before planning to make a big purchase, like a house or car. You can check your report annually for free by visiting annualcreditreport.com