The Ultimate Guide to Credit Cards
Tuesday, June 28, 2022

“How to Calculate Credit Card Interest” (3 Steps to Find Your Rate)

How To Calculate Credit Card Interest

credit card advice

Eric Bank

Written by: Eric Bank

Eric Bank

Eric Bank has been covering business and financial topics since 1985, specializing in taking complex subject matters and explaining them in simple terms for consumer audiences. In addition to his work on CardRates.com, Eric has appeared regularly on Credible.com, eHow, WiseBread, The Nest, Get.com, Zacks, Chron and dozens of other outlets. A former software engineer, Eric holds an M.B.A. from New York University and an M.S. in finance from DePaul University.

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Edited by: Lillian Guevara-Castro

Lillian Guevara-Castro

Lillian brings more than 30 years of editing and journalism experience. She has written and edited for major news organizations, including The Atlanta Journal-Constitution and the New York Times, and she previously served as an adjunct instructor at the University of Florida. Today, she edits all CardRates content for clarity, accuracy, and reader engagement.

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Advertiser Disclosure

One of the most important factors in choosing a credit card is its interest rate, and it’s also important to know how to calculate credit card interest. All credit cards must disclose their annual percentage rate, or APR, which expresses their interest rates in a single annual number. Almost all credit cards charge interest only on balances that you don’t fully pay off in the most current billing cycle. But how does APR translate into the amount of interest you’ll actually pay?

Read on to learn more about, including an in-depth look at how you can find your daily periodic rate, simple versus compound interest, how to calculate your average daily balance, and more. Or skip ahead to learn how your APR is calculated or to compare the best balance transfer offers to avoid paying interest.

Step 1: Divide APR by 360 (or 365) to Find Out Your Daily Periodic Rate

Before we can explain the first step, we should clarify a few important terms:

Grace Period: The normal billing cycle for a credit card can range from 28 to 31 days. The due date for your monthly payment is no less than 21 days after the end of the billing cycle. Each billing cycle provides a grace period, which means you don’t incur interest on purchases made within the billing cycle if you pay them in full by the due date. Your outstanding balance is the accumulated amount you haven’t paid within a grace period.

Simple Versus Compound Interest: Simple interest is the amount you pay on your outstanding balance without including the effect of compounding. Virtually all cards figure your interest with compounding, which means they add the interest you already owe to the amount subject to interest – you are paying interest on interest.

In the good old days, credit cards used monthly compounding, but the current fashion is daily or continuous compounding, which will cost you more. As an example of daily compounding, if your outstanding balance is $1,000 and the day’s interest is 71 cents, then tomorrow’s outstanding balance will be $1,000.71 (assuming no other purchases or payments).

Nominal Versus Effective APR: When you see an ad for a credit card, the interest rate is expressed as the nominal APR, which is based on simple interest and excludes fees. The more appropriate number is the effective APR, which includes the effects of compounding and any fees that are not paid separately. Some cards charge the annual fee (if any) as a lump sum, but others spread the annual fee over the entire year, making it part of the effective APR.

If possible, obtain the effective APR of any credit card you are considering. Fees for late payments or for exceeding your credit limit are not included in any APR, since they are charged separately.

To illustrate the three-step process for calculating your interest charges, imagine that you have an outstanding balance of $3,500 on a credit card with an interest rate of 25 percent.

In this example, the credit card uses a 360-day year (some cards use 365, terms will vary), so the daily percentage rate, or DPR, is equal to 25% / 360, or .06944%. This is the interest rate you pay each day on the balance subject to interest. Assuming daily compounding and no other activity, your daily balance would grow each day by the interest charged on the previous day.

Step 2: Calculate Your Average Daily Balance

The average daily balance is computed by adding together each day’s outstanding balance and dividing by the number of days in the billing period. For simplicity’s sake, we set the average daily balance to $3,500.

Step 3: (Avg. Daily Balance x DPR) x Days in the Month

Finally, we calculate the interest charged for the billing cycle, which in this example, is $3,500 x .06944% x 30 days, or $72.91. This is the amount of interest you would be charged on a card with a $3,500 balance and a 25% interest rate.

How Banks Determine Your APR

The APR on your credit card is based on the bank’s opinion of your creditworthiness, which is in large part derived from your credit score. Most banks use FICO credit scores, which range from 300 (the worst) to 850 (the best).

Each of the three major credit bureaus, Equifax, Experian, and TransUnion figure their FICO scores a little differently, but the scores tend to cluster closely. Interpretations differ, but generally, 700 is considered the dividing line between good and fair scores. The lower the score, the higher APR you’ll pay. If your score is too low, you could have difficulty qualifying for any credit at all.

Sometimes, banks will take into account other factors when determining your APR, such as black marks on your credit history (bankruptcies, court decisions, garnished wages, etc.). You will save money on interest if you can raise your FICO score – check out the myFICO website for tips on how to do that.

Delay Interest Payments with a Balance Transfer Offer

Many credit cards offer special balance transfer deals that can save you money. In a balance transfer, you move your outstanding balance from one credit card to another. To entice new customers, the balance transfer offers usually include a set number of months during which you don’t owe any interest on the transferred amount.

Some of the best balance transfer offers grant interest-free periods of 15 or even 21 months. In addition, some cards will also grant a multi-month grace period on new purchases made after you transfer a balance. If you combine that with a zero-percent annual fee and a reasonably low APR, you have the makings of a great credit card. Here are some of our favorites:

Discover it® Balance Transfer Review

at Discover Card'ssecure website

0% BALANCE TRANSFER RATING

★★★★★
5.0

OVERALL RATING

  • INTRO OFFER: Unlimited Cashback Match – only from Discover. Discover will automatically match all the cash back you’ve earned at the end of your first year! There’s no minimum spending or maximum rewards. You could turn $150 cash back into $300.
  • Earn 5% cash back on everyday purchases at different places each quarter like Amazon.com, grocery stores, restaurants, gas stations and when you pay using PayPal, up to the quarterly maximum when you activate. Plus, earn unlimited 1% cash back on all other purchases – automatically.
  • NEW! Discover helps remove your personal information from select people-search websites. Activate by mobile app for free.
  • Redeem cash back any amount, any time. Rewards never expire.
  • No annual fee.
  • Click "Apply Now" to see terms and conditions.
Intro (Purchases)
Intro (Transfers)
Regular APR
Annual Fee
Credit Needed
0% Intro APR for 6 months
0% Intro APR for 18 months
12.74% - 23.74% Variable APR
$0
Excellent/Good/Average

0% BALANCE TRANSFER RATING

★★★★★
4.9

OVERALL RATING

  • No Late Fees, No Penalty Rate, and No Annual Fee... Ever
  • 0% Intro APR for 21 months on balance transfers from date of first transfer and 0% Intro APR for 12 months on purchases from date of account opening. After that the variable APR will be 16.24% - 26.24%, based on your creditworthiness. Balance transfers must be completed within 4 months of account opening.
  • There is a balance transfer fee of either $5 or 5% of the amount of each transfer, whichever is greater.
  • The standard variable APR for Citi Flex Plan is 16.24% - 26.24%, based on your creditworthiness. Citi Flex Plan offers are made available at Citi's discretion.
  • Stay protected with Citi® Quick Lock and $0 liability on unauthorized charges
Intro (Purchases)
Intro (Transfers)
Regular APR
Annual Fee
Credit Needed
0% Intro APR Period 12 months on Purchases
0% Intro APR Period 21 months on Balance Transfers
16.24% - 26.24% (Variable)
$0
Excellent, Good Credit

Additional Disclosure: Citi is a CardRates advertiser.

0% BALANCE TRANSFER RATING

★★★★★
4.9

OVERALL RATING

  • 0% Intro APR for 21 months on balance transfers from date of first transfer and 0% Intro APR for 12 months on purchases from date of account opening. After that the variable APR will be 15.24% - 25.24%, based on your creditworthiness. Balance transfers must be completed within 4 months of account opening.
  • There is a balance transfer fee of either $5 or 5% of the amount of each transfer, whichever is greater
  • Get free access to your FICO® Score online.
  • With Citi Entertainment®, get special access to purchase tickets to thousands of events, including concerts, sporting events, dining experiences and more.
  • The standard variable APR for Citi Flex Plan is 15.24% - 25.24%, based on your creditworthiness. Citi Flex Plan offers are made available at Citi's discretion.
Intro (Purchases)
Intro (Transfers)
Regular APR
Annual Fee
Credit Needed
0% 12 months on Purchases
0% 21 months on Balance Transfers
15.24% - 25.24% (Variable)
$0
Excellent, Good

Additional Disclosure: Citi is a CardRates advertiser.

0% BALANCE TRANSFER RATING

★★★★★
4.8

OVERALL RATING

  • Start off strong with 0% Intro APR for 18 months from account opening on purchases and balance transfers. A variable APR of 15.74% - 24.49% on balance transfers and purchases after the introductory period ends.
  • Lower your interest rate by 2% each year. Automatically be considered for an APR reduction when you pay on time, and spend at least $1000 on your card by your next account anniversary.
  • Raise your credit limit. Get an automatic, one-time review for a higher credit limit when you pay on time, and spend $500 in your first six months.
  • All for no annual fee - You won't have to pay an annual fee for all the great features that come with your Slate Edge℠ card
  • Keep tabs on your credit health - Chase Credit Journey helps you monitor your credit with free access to your latest score, real-time alerts, and more
Intro (Purchases)
Intro (Transfers)
Regular APR
Annual Fee
Credit Needed
0% Intro APR on Purchases 18 months
0% Intro APR on Balance Transfers 18 months
15.74% - 24.49% Variable
$0
Good/Excellent

0% BALANCE TRANSFER RATING

★★★★★
4.8

OVERALL RATING

  • Earn 2% on every purchase with unlimited 1% cash back when you buy, plus an additional 1% as you pay for those purchases.
  • To earn cash back, pay at least the minimum due on time.
  • Balance Transfer Only Offer: 0% intro APR on Balance Transfers for 18 months. After that, the variable APR will be 15.49% - 25.49%, based on your creditworthiness.
  • Balance Transfers do not earn cash back. Intro APR does not apply to purchases.
  • If you transfer a balance, interest will be charged on your purchases unless you pay your entire balance (including balance transfers) by the due date each month.
  • There is an intro balance transfer fee of 3% of each transfer (minimum $5) completed within the first 4 months of account opening. After that, your fee will be 5% of each transfer (minimum $5).
  • The standard variable APR for Citi Flex Plan is 15.49% - 25.49%, based on your creditworthiness. Citi Flex Plan offers are made available at Citi's discretion.
Intro (Purchases)
Intro (Transfers)
Regular APR
Annual Fee
Credit Needed
N/A
0% Intro APR Period 18 months on Balance Transfers
15.49% - 25.49% (Variable)
$0
Excellent, Good

Additional Disclosure: Citi is a CardRates advertiser.

+See more balance transfer cards

Pay Your Balance in Full to Avoid Interest Altogether

Now that you know how interest is calculated, you can follow this strategy to lower your interest expenses:

  1. Improve your credit score
  2. Shop around for a credit card that combines the lowest effective APY with the best balance transfer program
  3. Transfer debt from other credit cards to your new one
  4. Pay down your credit card debt during the 0% interest intro period of your balance transfer
  5. Avoid accumulating outstanding balances in the future

For almost all credit cards, you’d never shell out any interest if you paid off your balance in full each month. However, some credit cards do not provide grace periods, so it’s worth the extra effort to look into this before applying. One other point – cash advances incur interest immediately and never have a grace period, so if you’re looking to avoid interest, that may not be the route for you.

Advertiser Disclosure

CardRates.com is a free online resource that offers valuable content and comparison services to users. To keep this resource 100% free, we receive compensation for referrals for many of the offers listed on the site. Along with key review factors, this compensation may impact how and where products appear across CardRates.com (including, for example, the order in which they appear). CardRates.com does not include the entire universe of available offers. Editorial opinions expressed on the site are strictly our own and are not provided, endorsed, or approved by advertisers.