Your FICO score is one of the most important numbers in your life.

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.

This is the number lenders look at when you apply for a mortgage, auto loan or credit card. (Click here to find out more about what goes into your FICO score.)

The best place to get yours is Fair Isaac.

It will provide a credit history from two of the three major credit-reporting agencies -- TransUnion and Equifax -- and your FICO score based on that report, when you order its FICO Standard package for $15.95.

The third major credit-reporting agency, Experian, ended its partnership with Fair Isaac in early 2009.

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

Be very careful about credit scores you get from any other source, especially the credit agencies.

They often sell credit scores derived from other scoring systems, such as the PLUS Score and VantageScore, so that they don't have to pay a royalty to Fair Isaac for using its equation.

These scores use different equations that can only approximate your FICO score and are never used by lenders or anyone else evaluating your creditworthiness.

Any Web site or ad that's trying to sell you a "credit score" without specifying that it's your "FICO score" is peddling a potentially misleading substitute.