Credit card interest rates are variable, meaning they fluctuate based on external factors like the prime rate. The prime rate is the interest rate banks charge their most creditworthy customers and is often used as a benchmark for setting credit card rates. When the prime rate increases, your credit cardit's interest rate can increase as well, which can make carrying a balance more expensive. It's important to monitor changes in the prime rate, especially if you carry a balance, as it will affect how much interest you'll end up paying.

In addition to the prime rate, other factors such as changes in your credit score or a missed payment can also cause your credit card interest rate to increase. Many credit cards have a penalty APR, which is a higher interest rate triggered by a late payment or other breach of the card's terms. To avoid this, it's crucial to make payments on time and monitor your credit score regularly to ensure that you qualify for the lowest available rates.