Today, mortgage interest rates, credit car and auto loan interest rates are all credit score driven.  The three credit reporting services -- Experian, TransUnion and Equifax --  have formulas that develop your credit score based on the information received from your creditors.  Some of the factors used to determine your credit score are:

     Number of accounts (home loans, credit cards, car loans, etc.)
     Number of late payments
     Proportion of balances to credit limits on revolving accounts
     Collections and bankruptcies
     Length of time accounts have been established
     Length of credit history
     Types of credit 
     Number of credit inquiries
     Too many accounts with balances
     Too many accounts without balances

Credit scores and be as low as 400 and as high as 900.  A creditor can use the credit score of one reporting service or all three.  It is rare that all three services will compute the same credit score, so creditors like to use the middle of the three scores.  This is especially true of mortgage lenders.  Ultra-preferred rates are reserved for individuals with a middle score above 740.  If your score falls between 680 and 739, you will still qualify for a preferred rate.  An individual with a score between 640 and 679 will usually pay a higher interest rate.  If your score falls below 640, you will probably have to pay a significantly higher interest rate in order to obtain credit.