Your credit score is calculated by applying a mathematical algorithm to the information on your credit report. It's a fairly complex and largely proprietary process. Your scores will likely fluctuate each time the data in your credit reports changes.
There are five main criteria that make up your score: Your payment history, debts, credit age, your account diversity, and inquiry history.
Payment History -- 35% (roughly 298 available points)
How Long You've Had Credit (Credit Age) -- 15% (roughly 127 available points)
Variety of Accounts (Account Diversity) -- 10% (roughly 85 available points)
Your Efforts to Get New Credit (Inquiry History) -- 10% (roughly 85 available points
Information on your credit file is deemed as being predictive of credit risk and is legal to use. The information on your credit files has a certain value to it when it comes to determining credit risk.