A person's credit card balances will determine 30% of the credit score. This amount equals 255.0 of the 850 FICO points. This one segment (of the five segments) of the credit score is the easiest method for someone to both IMPROVE and WORSEN their own credit score.
Here's how it works. The scoring system takes the balance at the time of the report (say $550) and divides it into the available credit limit (say $1000). This person is therefore given a 55.0 % balance or utilization ratio. That type of score is below average and will lower the credit score. There are certain balance ratios that help or hurt the score. 0% to 29% are very good for your credit score. 30% to 49% is mildly helpful to your credit score. 50% to 79% is mildly hurtful to the credit score. 80% to 100% is very, very bad for the credit score.
The moral of the story? Always keep your credit card balances under 30% if you want lots of those 255.0 credit scoring points to be awarded to you.