From the wikipedia entry on Credit Score:
Credit scores are designed to measure the risk of default by taking into account various factors in a person's financial history. Although the exact formulas for calculating credit scores are closely guarded secrets, the Fair Isaac Corporation has disclosed the following components and the approximate weighted contribution of each:
35% — punctuality of payment in the past (only includes payments later than 30 days past due)
30% — the amount of debt, expressed as the ratio of current revolving debt (credit card balances, etc.) to total available revolving credit (credit limits)
15% — length of credit history
10% — types of credit used (installment, revolving, consumer finance)
10% — recent search for credit and/or amount of credit obtained recently
The above percentages provide very limited guidance in understanding a credit score. For example, the 10% of the score allocated to "types of credit used" is undefined, leaving consumers unaware what type of credit mix to pursue. "Length of credit history" is also a murky concept; it consists of multiple factors — two being the oldest account open and the average length of time an account has been open. Although only 35% is attributed to punctuality, if a consumer is substantially late on numerous accounts, his score will fall far more than 35%. Bankruptcies, foreclosures, and judgments affect scores substantially, but are not included in the somewhat simplistic pie chart provided by Fair Isaac.
Current income and employment history do not influence the FICO score, but they are weighed when applying for credit. For instance, an unemployed individual with no other sources of income will not usually be approved for a home mortgage, regardless of his or her FICO score.
There are other special factors which can weigh on the FICO score.
Any monies owed because of a court judgment, tax lien, or similar carry an additional negative penalty, especially when recent.
Having more than a certain number of consumer finance credit accounts also carries a negative weight (critics say that this causes a vicious cycle, locking people into continuing to use consumer finance companies).
The number of recent credit checks also can weigh down the score, although credit agencies usually claim to allow for credit checks made within a certain window of time to not aggregate, so as to allow the consumer to shop around for rates.
For more information about factors that may influence your credit score read the credit rating section of the credit history page.
