To best understand how the score is computed you need to understand that the FICO score is made up of 5 main factors that are all weighted differently. This means that some factors like payment delinquency is weighted more heavily than say, inquiries for new credit. While this makes common sense, by understanding how the computer scores different factors you will have a better shot at making the changes that will have the maximum impact to your score.
Factor 1: Payment History - 35% of Score
It is easy to understand why your payment history is weighted so heavily as it is this information that tells a prospective creditor what your history has been paying your other creditors. This information gives prospective lenders insight as to how you will likely treat their account based on your previous payment history.
When it comes to derogatory credit information (often referred to as "dings") the assignment of weight (how much your score will decline) is based on three factors:
Recency refers to how recent (from the time of credit report being pulled) the "ding" was reported. For example, if you had a 30-day late on a credit card only one month ago, this would score more heavily (more negatively) than a 30-day late that was reported last year. As far as regular payment "dings" (30, 60 & 90 day lates) the time scale is 24 months. This means that the more recent the "ding" to the date that the report was pulled, the more it hurts your score. The closer the "ding" to the 24 month (back) date, the less it will impact your score negatively. And when the standard 30, 60, or 90-day late becomes over 2yrs old it is NO LONGER PART OF THE SCORE! While you can still READ the information on the report (for up to 7 years) the "ding" is no longer being calculated as part of your score. This is important, because for most people, if you start doing the right things with your credit and pay your bills on time, you can go from bad credit to good credit, even great credit within 2 years.
Frequency refers to how often you have payment "dings". If you have one 30-day late in the last 24 months, this will hurt your score less than if you had 2 or more late payments in the last 24 months. So the fewer the late payments within a 2 year period, the better!
Severity refers to the type of derogatory information or "ding". A 30-day late is worse than past-due. A 60-day late is worse than a 30-day late and a 90-day late is worse than a 60-day late. Nothing is worse than a 90-day late because credit card companies have determined that most 90-day late accounts end up having to be "charged off" and end up in collections. In fact the true definition of the original FICO score was "What is the likelihood that a borrower will have a 90-day late in the next 24 months?" Try to avoid 90-day lates at all costs as this type of "ding" is weighted the most heavy and negatively affects your score more than the others. However, as with 30-day and 60-day lates, after the "ding" is over 24 months old, it is no longer part of the active score.
Factor 2: Balance of Available Credit - 30% of Score
The second largest factor affecting your credit score, next to your delinquent payment history is related to your balances relative to your credit limits. It is important that you understand how this works. Let's say you have a VISA card with a $10,000 limit. If your balance on that credit card is $6,000, although you are not maxed-out...you will suffer a "ding" to your credit. Fair Isaac will not release the details of exactly how much it hurts your score, but it is generally accepted that like the rest of credit scoring, it is based on a sliding scale.
The closer to maxed-out the worse the "ding" to your score. Again, although Fair Isaac has not released the details, many industry experts believe that the optimal ratio of balance to available credit is 30%. It is also generally assumed that the "ding" becomes more severe as you cross the 50% line and head towards the max. This ratio is applied per card not against your total credit limit across all cards. For example, if you had 4 credit cards each with $10,000 limits, the system will look at the balance ratio on each card and then assign a point value. The reason that this is important is that many people might have several credit cards that have no balance and that they rarely, if ever use. Then they have one or two cards that they use all the time. Let's say that out of the 4 cards I mentioned previously, Jane only carries a balance on one the cards and leaves the other three with no balance. If card one had a balance of 8,000, although that only represents 20% of her total available credit ($40,000) it actually represents an 80% ratio for that specific card, and that is how the system is looking at that. So Jane would be better off (from a credit score perspective) to spread $2,000 onto each card thereby reducing her ratio to only 20% per card. The reason is that there is NO positive points awarded for carrying no balance, only negative points for the 80% ratio on the one card that Jane uses.
So she was "dinged" for the one card she uses, but received no compensating positive points for the three cards that she carried no balance. An important distinction to make is that credit scoring decisions may be counter to financial decisions. For example, if Jane only used card #1 because it had a very low interest rate compared to her three other cards, this would be a good financial decision. However, as we have just learned this will cost her in FICO points. So you need to make your decision based on what your goal is. If you have excellent credit and have points to spare (i.e. 750) then you may choose to use Jane's strategy and save money on interest charges. If on the other hand you are trying to improve your credit while you apply for a loan or a new credit card, you would want to spread the money to all the cards to avoid the "ding" from the 80% ratio on card #1.