Factors that affect the APR on your credit card include:
The prime rate. Credit card interest rates are often linked to the prime rate, which is the interest rate that banks charge their biggest and best customers. The APR on a credit card might be set as "prime + 10%" or "prime plus 12%." If the prime rate were 5%, those standards would equate to an APR of 15% or 17%. When the prime rate goes up, so do these cards' APRs. When the prime rate goes down, so do these cards' APRs.
Risk. Cards designed for people with subpar credit, or for people who are new to credit, will generally charge higher interest rates because lending money to these consumers is riskier than lending to people with excellent scores and established credit histories. Cards that advertise low ongoing rates are generally only available to those with good credit.
Rewards. Cards that offer rewards on purchases, such as cash back or travel points, generally charge higher interest.
Your credit score. Some cards charge a single interest rate; others charge a range of rates. The rate you get — either within a range or just by qualifying for the card in the first place — is influenced by your credit score.
Transaction types. A credit card might charge different APRs for different types of balances. Purchases may be charged interest at one rate, cash advances at another, and so on.