The most widely used credit score is the FICO score, was developed by Fair Isaac & Company, Inc. (and they're named after their inventor!). There are now two other major providers of credit scores.  Your credit score is between 350 (high risk) and 850 (low risk).

Credit scores only consider the information contained in your credit profile.  They do not consider your income, savings, down payment amount, or demographic factors like gender, race, nationality or marital status.  In fact, the fact they don't consider demographic factors is why they were invented in the first place.

"Profiling" was as dirty a word when credit scores were invented as it is now.  Credit scoring was developed as a way to consider only what was relevant to somebody's willingness to repay a loan.

Past delinquencies, derogatory payment behavior, current debt level, length of credit history, types of credit and number of inquiries are all considered in credit scores.  Your score in essence starts out with a perfect score and then deducts from there.  This is the reason why when a mortgage tri-merge credit report is ran, there is always three negatively worded factors given why the scores were lowered from perfect.

Different portions of your credit history are given different weights.  Thirty-five percent of your credit score is based on your specific payment history.  Thirty percent is your current level of indebtedness.  Fifteen percent each is the time your open credit has been in use (ten year old accounts are good, six month old ones aren't as good) and types of credit available to you (installment loans such as student loans, car loans, etc. versus revolving and debit accounts like credit cards).  Finally, five percent is pursuit of new credit -- credit scores requested.

Your credit report must contain at least one account which has been open for six months or more, and at least one account that has been updated in the past six months for you to get a credit score.  This ensures that there is enough information in your report to generate an accurate score.  If you do not meet the minimum criteria for getting a score, you may need to establish a credit history prior to applying for a mortgage.

The mortgage industry uses all three credit scores to determine what score is most relevant to underwriting your home loan.  We typically drop the high and the low score and use the middle one.  When two people buy together, typically the lower of the two middle scores is used.  In some cases, the middle score of the individual making the most money is used but again, this method is not widely used.