Ever wonder why you can go online and be approved for credit within 60 seconds? Or get pre-qualified for a car without anyone even asking you how much money you make? Or why you get one interest rate on loans, while your neighbor gets another?

The answer is credit scoring.

Your credit score is a number generated by a mathematical algorithm -- a formula -- based on information in your credit report, compared to information on tens of millions of other people. The resulting number is a highly accurate prediction of how likely you are to pay your bills.

If it sounds arcane and unimportant, you couldn't be more wrong. Credit scores are used extensively, and if you've gotten a mortgage, a car loan, a credit card or auto insurance, the rate you received was directly related to your credit score. The higher the number, the better you look to lenders. People with the highest scores get the lowest interest rates.

Scoring categories
The scale runs from 300 to 850. The vast majority of people will have scores between 600 and 800. A score of 720 or higher will get you the most favorable interest rates on a mortgage, according to data from Fair Isaac Corp., a California-based company that developed the credit score. (Its own score is called the FICO score.)

American public's credit scores break out along these lines:

Credit score Percentage 499 and below 1 percent 500-549 5 percent 550-599 7 percent 600-649 11 percent 650-699 16 percent 700-749 20 percent 749-799 29 percent 800 and above 11 percent

What's the big deal?
Your credit score will determine if you get credit at all, and the interest rate on that credit, says Ed Ojdana, president of Experian Consumer Direct, part of Experian, the largest of the three major credit-reporting agencies. "The better the score, the lower the interest rate and that can save you a ton of money."

The difference in the interest rates offered to a person with a score of 520 and a person with a 720 score is 3.45 percentage points, according to Fair Isaac's Web site. On a $100,000, 30-year mortgage, that difference would cost more than $85,000 extra in interest charges, according to Bankrate.com's mortgage calculator. The difference in the monthly payment alone would be about $235.