How Is Credit Card Interest Calculated?

APR and interest rate mean the same thing here

On a credit card, the annual percentage rate (APR) and the interest rate are effectively the same number. That is different from a mortgage or auto loan, where APR folds in extra costs. Credit card fees like annual fees and cash advance fees sit outside the APR, so the rate you see is the rate used to calculate interest on your balance.

One catch: most cards carry a variable APR tied to the prime rate. When the Federal Reserve moves rates, your APR can follow. For reference, the Federal Reserve reported an average credit card APR of about 21% in the second quarter of 2026, so a rate in the low twenties is normal territory. See the full breakdown of the average credit card APR.

Step one: turn the APR into a daily periodic rate

Interest doesn't get charged once a year. It is charged every day. To do that, your issuer divides your APR by 365 to get the daily periodic rate. Some issuers divide by 360 instead, which your cardholder agreement will specify. The Consumer Financial Protection Bureau uses 365 as the standard.

So a 24.99% APR becomes a daily periodic rate of 24.99% ÷ 365, which is about 0.06847% per day. Small, until you multiply it by a balance and 30 days.

Step two: the average daily balance method

Here is the part most people miss. Issuers don't usually charge interest on your balance as of one moment. They use the average daily balance. They add up your balance at the end of every day in the billing cycle, divide by the number of days, and apply the daily rate to that average across the cycle. Because purchases and payments move your balance around during the month, the average is what actually gets charged.

And because most issuers add each day's interest to the balance before calculating the next day, credit card interest compounds daily. That means you pay a little interest on yesterday's interest, which is why a carried balance grows faster than a flat annual rate would suggest.

A worked example

Take a $3,000 balance at 26.99% APR over a 30-day cycle, assuming the balance doesn't change:

• Daily periodic rate: 26.99% ÷ 365 = 0.07394% per day
• Interest per day: $3,000 × 0.0007394 = $2.22
• Interest for the cycle: $2.22 × 30 = about $66.55

That is the answer to a very common question, "how much is 26.99% APR on $3,000?" It is roughly $66 a month in interest alone. Our Credit Card Interest Calculator runs this for any balance and rate, and shows the daily periodic rate it used so you can see the math.

The grace period: how to pay zero interest

You aren't charged interest on purchases automatically. Most cards give you a grace period, usually 21 to 25 days between the end of the billing cycle and your due date. Under the CARD Act of 2009, if a card offers a grace period it must be at least 21 days. Pay your full statement balance by the due date and you owe no interest on purchases, full stop.

The grace period only holds if you pay in full. Carry a balance and you typically lose the grace period until you are caught up, which means new purchases can start accruing interest right away. Two things never get a grace period: cash advances and most balance transfers.

More tactics in our guide on how to avoid credit card interest. If you have never carried a balance yet, this guide to when interest actually starts walks through protecting your grace period from your very first statement. And if you're hoping interest paid comes with a tax break, it usually doesn't, see is credit card interest tax deductible.

The APR types that change the math

Your card may apply several different APRs depending on how you use it:

• Purchase APR: the everyday rate on things you buy.
• Cash advance APR: usually higher than the purchase rate, with an upfront fee and no grace period, so interest starts the day you take the cash. This is one of the most expensive ways to use a card. See what a cash advance really costs.
• Balance transfer APR: the rate on a balance moved from another card, often a low or 0% promotional rate with a 3% to 5% transfer fee. See if a balance transfer saves you money.
• Penalty APR: a higher rate, sometimes up to around 29.99%, that an issuer can apply after a late payment. Federal law requires 45 days' notice, and it can stick around for at least six months.
• Introductory / 0% APR: a promotional rate for a set period. When it ends, the regular APR applies to any remaining balance. Watch for deferred interest on store cards, where failing to clear the balance in time can make you owe all the interest retroactively.

For the full breakdown of each rate and when it applies, see the types of credit card APR.

Why minimum payments cost so much

Because interest is charged on your whole balance but the minimum payment is only a small slice of it, most of an early minimum payment goes to interest, not principal. Worse, the minimum is usually a percentage of the balance, so it shrinks as the balance shrinks, stretching payoff over years. On a $5,000 balance at 24% APR, paying only the minimum can take around 17 years and cost more in interest than the original balance. Our Minimum Payment Calculator shows exactly how long, and how much a fixed payment saves.

How to pay less interest

• Pay in full within the grace period. The single most effective move. No carried balance, no purchase interest.
• Pay more than the minimum, at a fixed amount. Freezing your payment instead of letting it shrink can cut years off a balance.
• Use a 0% intro APR wisely. Good for a large purchase or a balance transfer, as long as you clear it before the promo ends.
• Avoid cash advances. No grace period plus a higher rate plus a fee is the worst combination.
• Ask for a lower APR. A call to your issuer, especially with a clean payment history, sometimes works.

Run your own numbers

• Credit Card Interest Calculator →See what a balance actually costs in interest per day, cycle, and year.
• Credit Card Payoff Calculator →Your payoff date and total interest, with an optional extra payment.
• Minimum Payment Calculator →How slow the minimum really is, and what a fixed extra payment saves.

Related guides

• How to Pay Off Credit Card Debt →A step-by-step plan: list your debts, pick an order, run the numbers.
• How to Lower Your Interest Rate →A script for calling your issuer, plus what to do if they say no.
• How to Avoid Credit Card Interest →Pay zero interest by using the grace period correctly, every cycle.
• Types of Credit Card APR →The five APRs a card can charge, and which one applies to your balance.
• What Is a Penalty APR? →What triggers a penalty APR, how high it goes, and how to get your rate back.
• 0% Intro APR and Deferred Interest →A true 0% offer versus a deferred-interest trap, and how to tell them apart.
• Debt Avalanche vs Snowball →Which payoff order saves more money, and which keeps you motivated.
• Average Credit Card APR →The current average APR, and how to tell if your own rate is high.