It rates your creditworthiness on a scale of 300 to 850 using your credit history and a widely accepted formula developed by Fair Isaac Corp.

That's the number lenders look at.

The best place to go is Fair Isaac. It will provide a credit history from one of the major credit-reporting agencies, and your FICO score based on that report, when you order its FICO Standard package for $15.95.

(Experian has just ended its contract with Fair Isaac and you can no longer get a score based on its credit report through the FICO Web site. But you can still get credit scores based on your TransUnion and Equifax credit reports.)

A cheap but less informative alternative is to get a free estimate of your FICO score from Fair Isaac.

Equifax also will sell you your credit history and FICO score through its Score Power package for $15.95.

Don't go to Experian and TransUnion.

They sell consumers a credit score, but it's not your FICO score. It is a VantageScore, which is calculated using a new system Experian, TransUnion and Equifax created to compete with FICO.

Their system rates your credit on a scale of 501 to 990, which means your VantageScore is almost always higher than your FICO score. No major lender uses VantageScores when evaluating potential borrowers.