There are many factors that go into a credit score, but the debt utilization ratio may be the one that confuses people the most. “I think this is one of the most important terms people need to know, but they don’t,” Exantus says. The debt utilization ratio refers to how much of a person’s available credit is being used. For instance, a person who has maxed out their available credit has a 100 percent debt utilization ratio. Someone who doesn’t have any debt charged to their credit cards has a zero percent debt utilization ratio. Exantus notes once you exceed a 30 percent ratio, it can begin to negatively affect your credit.