Credit usage represents how much of your standing credit balance you are using on average. This means that if between credit lines and credit cards you have available credit for $10k, and you use $2,000 your usage would be 20%. Even though there is not a magic number, it is important to always remember that the higher the usage the more it will affect your credit score. Many experts and financial advisors recommend to never exceed 30% at any time, this will ensure that you won't be affecting your credit rating. The idea behind having credit is to take advantage of it, having lots of credit lines and credit cards unused will do even more harm to your score than if there were used properly.