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How does credit card interest work?

Understand interest so you can apply for credit cards with confidence.

People make a big deal out of interest rates when applying for credit cards. They tell you interest is important, and that you should carefully compare rates between credit cards.

They’re right, of course. But why are interest rates so important? More fundamentally, what is interest?

In this guide, we demystify how credit card interest works.

What is interest?

Interest is what you’re charged for borrowing money.

When you make a purchase on your card, you’re borrowing money from your credit card company. Instead of carrying around $300 in cash to buy a new TV, you swipe your card and pay your card provider back later.

When your credit card bill arrives, you have two options:

  • Pay back what you owe in full.
  • Pay back a portion of what you owe and continue to carry a balance on your credit card.

If you choose to carry a balance on your card — meaning you’re continuing to borrow money — your card provider isn’t going to let you do it for free. For the privilege of borrowing money, you pay your provider interest.

Is APR the same as interest rate?

In the context of credit cards, APR and interest rate are the same.

Interest rate refers to the charges you’ll pay only for a principal — or the amount you borrow. The APR covers the interest rate as well as other costs.

For other financial products, these costs might include origination fees and discount points. This isn’t the same for credit cards — which is why the terms APR and interest rate are interchangeable. Annual fees are listed upfront in fee tables, and costs such as late fees and balance transfer fees will vary by cardholder.

What is ongoing APR?

The ongoing APR is the interest rate that applies to your purchases, balance transfers or cash advances throughout the year and outside of a 0% intro APR period.

How is the interest rate determined?

Credit card issuers typically set interest rates for each customer based on the prime rate plus an additional percentage.

For example, the prime rate might be 5%. A card provider might add an additional 12% of interest, giving you an APR of 17%. Because the prime rate can change, this APR is said to be variable. Some credit cards offer fixed rates, though this is a lot less prevalent.

This credit card prime rate is directly influenced by changes to the federal funds rate set by the Federal Reserve. So if the federal funds rate is slashed several times, as we’ve experienced recently, the credit card prime rate will often fall by a similar percentage to match. Similarly, increases to the federal funds rate will lead to greater credit card interest rates across the board.

Why is my APR so high?

While the prime rate plays a role in average interest rates, your provider ultimately determines your APR based on your creditworthiness. With a strong credit history, you’re more likely to qualify for a low interest rate since you’ve proven your ability to pay responsibly. With shakier credit, you’re more likely to receive a high interest rate because your issuer has no guarantee you’ll be able to pay back what you borrow. Late payments and other missteps can also increase your APR.

And, of course, credit card companies need to make some form of profit. Any interest you end up paying on your credit card goes right to the issuing bank. That’s why if you have a less than stellar credit history, you might find your interest rates higher than average: they’re banking on the idea that you might not pay your balance in full each month.

Types of credit card interest

There are various types of credit card interest you can accrue. These are the most common:

As you spend on your credit card, your debts will also begin to collect interest if you’re unable to pay the whole balance back by the end of the statement or interest-free period. If you’ve used your card for purchases, it will start collecting interest — typically up to around 25% APR.
If you’ve used your card for an ATM withdrawal or any other transaction that’s considered a cash advance, you’ll trigger the cash advance rate — typically up to around 27% APR.
If you decide to transfer your debt from one card to another — maybe another card offers a better APR — you’ll also accrue a balance transfer interest rate, which is usually the same as the purchase APR.
This is also known as an intro APR period on purchases or balance transfers. Usually, it’s available for a limited time, with the standard interest rate applying after that. For example, a card may offer you 0% interest on balance transfers for the first 12 months. If you didn’t pay off the balance transfer during the first 12 months, the standard rate for balance transfers would apply to the debt.

How interest is charged

Card companies express interest in the form of an APR or annual percentage rate. For example, your APR could be 17%, which is a standard interest rate across the industry.

This doesn’t mean your card provider charges you interest once a year. Instead, it applies your APR to your balance either every day or every billing cycle.

There are different methods of calculating interest. The biggest card companies generally use two methods: daily balance and average daily balance.

Let’s go over how these methods work.

The daily balance method

In your card’s terms and conditions, you may see this method written as “daily balance (including new transactions).” Because interest is calculated every day, your card company begins by finding your daily periodic rate. This is just your APR divided by 365, the number of days in a year.

Every day, your card company multiplies the daily periodic rate by your balance. That gives them your daily interest.


Card companies don’t always use 365 days to calculate your daily periodic interest rate. They sometimes use 360 days.

The card company adds that daily interest to your balance, resulting in your new current balance. Then the process starts over again the next day.

That’s the gist of it, but take a look at the math in the example below.

An example of the daily balance method

If your APR is 20%, your daily periodic rate will be 20% divided by 365 days — or .054795%. (That’s 0.00054795 on a calculator.)

Let’s say you’re carrying a $5,000 balance on your credit card.

Using interest calculations on Day 1:
  • You’ll be charged $5,000 x 0.00054795 — or $2.74 in interest.
  • That brings you to a new balance of $5,000 + $2.74 — or $5,002.74.
On Day 2:
  • You’ll be charged $5,002.74 x 0.00054795 — or $2.74 in interest.
  • That brings you to a new balance of $5,002.74 + $2.74 — or $5,005.48.

Now, let’s say you make a $200 purchase on Day 3.

With a $200 purchase, on Day 3:
  • Your new balance is $5,005.48 + $200 — or $5,205.48.
  • You’ll be charged $5,205.48 x 0.00054795 — or $2.85 in interest.
  • That brings you to a new balance of $5,205.48 + $2.85 — a total of $5,208.33.

Finally, let’s say you pay off $400 of your balance on Day 4.

With a payment of $400, on Day 4:
  • Your new balance is $5,208.33 – $400 — or $4,808.33.
  • You’ll be charged $4,808.33 x 0.00054795 — or $2.63 in interest.
  • That brings you to a new balance of $4,808.33 + $2.63 — or $4,810.97.

If you do nothing else on your credit card for the rest of the month (and we keep repeating the interest calculation), you’ll accrue $79.98 in interest for this billing cycle.

The process is tedious, but that’s how daily interest works.

How does this look over a calendar month?


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The average daily balance method

In your card terms, you may see this method written as “average daily balance (including new transactions).”

Like in our previous method, you start with finding your daily periodic rate.

Next, you find the average of all of your daily balances over the billing period. You do this by adding your balances for every day in the period divided by the number of days in the billing cycle.

Finally, you multiply your daily periodic rate by your average daily balance. Then you multiply the result by the number of days in the billing cycle. This gives you the interest you’ll pay for this billing cycle.

To clarify how this works, let’s go over an example.

An example of the average daily balance method

Like in our other example, let’s say you’re paying 20% APR on a $5,000 balance. Again, the daily periodic rate will be 20% divided by 365 days — or .054795%. (That’s 0.00054795 on a calculator.)

On Days 1 and 2, you don’t do anything with your card, so your balance is unchanged.

On Day 1:
  • Your balance is $5,000.
On Day 2:
  • Your balance is $5,000.

On Day 3, you make a $200 purchase.

With a $200 purchase, on Day 3:
  • Your new balance is $5,000 + $200 — or $5,200.

And on Day 4, you make a $400 payment toward your balance.

With a $400 payment, on Day 4:
  • Your new balance is $5,200 – $400 — or $4,800.

Let’s say you don’t use your card again for the rest of the month. That means on Days 1 and 2, your balance was $5,000; on Day 3 your balance was $5,200; and the balance for Days 4 through 30 was $4,800.

First, we’ll add up the balances for the month:

$5,000 + $5,000 + $5,200 + ($4,800 x 27 days) = $144,800

Then we’ll divide that number by the number of days in the billing cycle:

$144,800 / 30 = $4,826.67
Our average daily balance is $4,826.67.

Now, we multiply our daily periodic rate, our average daily balance and the number of days in the billing cycle.

0.00054795 x 4,826.67 x 30 = $79.34
This means that in our next billing statement, we’ll see a $79.34 charge for interest.

How does this look over a calendar month?


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Must read: Compound interest costs

The way credit card interest is charged is known as “compound interest” because it is calculated daily. This means you could end up paying interest on your interest charges. The good news is you can cut down on interest costs any time you make a repayment because that will also affect the daily interest calculation.

But do you have to pay interest?

credit card interestOne misconception about interest is that you have to start paying it immediately. In fact, most credit card companies give you a grace period during which you can pay off your debt before interest kicks in.

Your card company should list the length of this grace period in its terms and conditions. Terms typically look something like:

Your due date will be a minimum of 21 days after the close of each billing cycle. We will not charge you interest on purchases if you pay your entire balance by the due date each month.

Here are a few examples of how that process works.

Example 1: You pay off your balance in full each month

Let’s say you’ve made $100 in purchases in the first month you open your card (we’ll say it’s January).

  • After the end of January (when your billing cycle ends), you’ll receive your credit card statement. You need to pay back that $100 you charged to your card.
  • Now you have a 21-day period to pay that $100. You pay off the $100 on February 15.

Since you owed $100 but then paid off $100, your balance is $0. In terms of interest, you’re free and clear for now.

There are benefits to this situation:

See the pattern? If you completely pay off your balance each month by the due date, you’ll never owe interest.

Example 2: You don’t pay off your balance in full each month

Again, let’s pretend you make $100 in purchases in the first month you open your card (January).

  • After the close of the billing cycle, you get a credit card statement for $100. On February 15, you pay only $50 toward your balance.

You owed $100 but paid off $50, so you’re still carrying a balance. There are disadvantages to this situation:

As you can see, this is one of the ways you can get into snowballing credit card debt. Carrying a balance can be dangerous, but there are ways to keep your balance down and avoid paying interest altogether.

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Compare low interest credit cards

1 - 3 of 6
Name Product Purchase APR Balance transfer APR Annual fee Filter values
PenFed Power Cash Rewards Visa Signature® Card
15.99% to 17.99% variable
2% cash back for all PenFed Honors Advantage members and 1.5% cash back on all purchases made with your card.
PenFed Platinum Rewards Visa Signature® Card
14.49% to 17.99% variable
Earn 5x points on gas at the pump and 3x points on groceries. Earn 1x points on all other purchases.
Capital One VentureOne Rewards for Good Credit
Capital One VentureOne Rewards for Good Credit
26.99% variable
26.99% variable
The same rewards and $0 annual fee as the Capital One VentureOne Rewards Credit Card, but for those with good credit.

Compare up to 4 providers

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The bottom line

We’ve made a lot of calculations in this guide to demonstrate how interest works. However, interest doesn’t really have to be that complicated. Your goal is to keep it as low as possible by paying off your balances as quickly as possible. Use our credit card repayment calculator to find out how long it will take to pay off your balance.

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Frequently asked questions

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