How to calculate credit card interest

Here at TPG, we always recommend paying off your credit card balances in full every month. Even the best rewards credit cards don't earn valuable enough rewards to offset the interest you'll be charged if you carry a balance.

But if you have a balance, it can be helpful to know how your interest is calculated to figure out how much you pay each month. The numbers on your statement can be confusing, though, and you may wonder, "How is credit card interest calculated?"

If that's the case, we have you covered. Here's what you need to know in order to figure out how much interest you will pay on a credit card.

Related: How to avoid and reduce credit card interest

How is credit card interest calculated?

Credit card interest is what the credit card company charges you to borrow money from them, which is what happens when you carry a balance. This interest is typically referred to as APR, which stands for "annual percentage rate." In other words, the APR is the amount of interest you'll accrue each year on your balance, plus any additional fees.

For example, if you have a credit card balance of $1,000 and your APR is 21%, you'll accrue $210 in interest over a year.

Related: What is a good APR for a credit card?

How to calculate credit card interest

Credit card interest typically accrues daily, so it's helpful to know how to calculate it based on whether you're charged daily or monthly; you aren't just charged one lump interest sum at the end of the year.

To break your APR down into monthly interest, divide the APR of 21% by 12. In this example of a $1,000 balance, your monthly interest rate is 1.75% or a monthly cost of $17.50.

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To break it down into daily interest, divide the APR by 365, giving you an interest rate in this example of approximately 0.06% or a daily cost of around 58 cents per day.

Of course, these numbers assume that you keep your balance at $1,000. If you pay down your balance each month, you'll accrue less interest. And if you charge more to your card or don't pay the interest as it accrues, your balance will increase, meaning the amount of interest you're charged will also increase.

Related: Are you paying enough attention to your credit card's APR?

Types of credit card interest

To make matters slightly more confusing, the credit card company might charge you different types of interest.

In the above example of calculating credit card interest, we assumed a "fixed rate" APR, which, as the term implies, is an interest rate that doesn't change.

However, many cards have a "variable rate" APR, meaning that your interest rate is subject to change monthly based on federal rates. If you have a variable rate APR, you'll want to look at your APR on your statement every month and recalculate your monthly interest when it changes.

Some cards also have a lower "promotional APR" for some time. If you have one of these, pay careful attention to the promotional period end date and calculate your monthly interest based on your new APR when it ends. Of course, if you can, the best strategy is to pay off your full balance during the promotional period and avoid paying any interest moving forward.

Related: Credit card debt hits new record of over $1 trillion — here's how to consolidate and pay off your debt

Bottom line

If you never look closely at your credit card bill, it's easy to assume that credit card interest is impossible to understand. However, now that you know how credit card interest is calculated, you can use this information to understand exactly how your annual, monthly and daily credit card interest amounts are calculated.

Related: The best way to pay your credit card bills