First the Federal Reserve decides on the prime rate and then your credit card issuer decides on the card’s margin, which is the percentage above the prime rate that a credit card charges.
The difference between what the credit card charges, and what the prime rate is, is called the margin. So, if the prime rate is 4% and your card’s APR is 15%, the margin is 11%.
Credit cards decide on the margin depending on your credit history. Those with an excellent credit score will likely have a lower margin than someone with a poor credit record.
Credit cards keep that margin for their customers, so if the Federal Reserve increases the prime rate by .25%, your card will likely increase your APR by the same percentage.