For many years, lenders have been deciding what interest rate they will charge, depending on a secret rating: your credit score.

Scores are supposed to make lenders more impartial and efficient, but consumers couldn't see their scores. Now, thanks to a growing consumer movement, borrowers will be able to get that once-secret information.

Fair, Isaac & Co., the California company that invented the formula, plans to make individual scores available to consumers through Equifax and Experian, two of the Big Three credit reporting bureaus that license its software. The third, TransUnion, is readying its own scores for release.

Scores are a number ranging from 300 to 900 that credit bureaus construct by plugging credit report data into the Fair, Isaac Software.

Fair, Isaac is revealing its list of factors that go into a score. The number of credit cards held affect a borrower's score, but it doesn't say what the right number is. Other factors that can hurt a score include the presence of new credit cards and the absence of car loans.

Finance company loans and many credit inquiries lower a score. No recent revolving balances lower scores of those chasing teaser rates or paying balances without paying interest.

The only way to 'fix' a credit score is by building a record of paying bills on time, all the time, and removing mistakes from your credit report.

It helps to pay down some debts before applying for a mortgage. If you have more than 10 credit cards, cancel a few. It's good to keep a couple of inactive cards. A customer with five cards, each with a $5,000 limit, who has a balance of $4,000 on one, will have a better rating if the balance is spread over all five. Keeping a small balance is better than no balance at all. Seven cards and four other loans are the average.

Fair, Isaac says 13 percent of credit scores are below 600; 11 percent rate 600 to 649; 16 percent from 650 to 699; 20 percent from 700 to 759; the largest group, 29 percent, rate from 750 to 799. And 11 percent stand at 800 or above.