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How to Calculate Interest on a Credit Card

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The true cost of your credit card depends on a range of factors, including how much you spend and how much and how often your card issuer charges interest on the unpaid balance.

It’s always a good idea to know exactly how much you’re paying every time you use your credit card. What may seem like an innocuous purchase could come back to haunt you down the line after you calculate the interest and other related fees. You should be aware of how much you will have to pay down the road when using a credit card, including how soon you will need to pay it off, the annual interest rate and any other guidelines for using the card. Use this guide to find out how much you’re really paying every time you swipe.

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How to calculate credit card interest

To determine the true cost of your credit card, you’ll need to calculate your credit card interest. Also, be aware that the credit card might have a promotional period with either a zero-percent or low interest rate. When you are calculating your annual percentage rate (APR), do not include this promotional period.

First, come up with the current outstanding balance on your credit card, or how much you still owe. You will find this on your latest credit card statement. You can also log into your account on the credit card issuer’s website for more information.

You will also need the annual interest rate. The company should include this information when you sign up for a card. It will also be printed on your credit card bill. The interest rate may be listed as APR. The interest rate may also change over time. Many credit card companies will advertise a lower interest rate for the first year or six months. A variable APR will then apply at the end of this trial period, so be sure you have the correct interest rate on hand.

Find the daily interest rate

It’s important to note that credit card companies charge interest by the day, not by year. That means you will accrue interest every day the debt remains outstanding, instead of taking on interest at the end of the year. Consult with your bank or credit union to find out the number of days that are included in the billing cycle. Some lending institutions may exclude holidays and weekends, which means the daily interest rate won’t be applied on these days.

To calculate credit card interest, divide your interest rate, or APR, by 365 for each day of the year. This is known as the daily periodic rate.

For example, if you have an APR of 6.5%, you will create this equation: 6.5%/365. The total is approximately 0.018% or 0.00018, which is your daily interest rate.

Find your average daily balance

The balance of your credit card will change from day to day as you continue to make payments and add new charges. Banks and credit unions use this information to calculate the daily interest rate.

For example, if the outstanding balance fluctuated between $1,000 and $1,500 last month, your average daily balance would be around $1,250.

Calculate the total interest

Once you have the daily interest rate and the average daily balance, multiply them together and then multiply that number by the number of days in the billing period.

For example, with an average daily balance of $1,250, a daily interest rate of 0.018%, and around 25 days in the billing period, the total daily interest would be around $5.625.

This number will vary based on how many compounding days there are in a period. Credit card companies use compound interest, which is the interest charged on the outstanding balance plus interest already accrued. Some credit card issuers will compound interest daily, while others do it monthly. Your outstanding balance will grow exponentially faster if the company compounds interest daily.

Before you apply for a credit card, you should have a clear idea of how long it will take you to pay it off. Use our interest rate calculator below to figure out how much you will owe.

How to reduce credit card interest

Reducing credit card interest comes down to two important factors, the total amount owed and the annual interest rate.

The credit card company will assign an interest rate based on your credit score and history. This number tells the company how likely you are to pay off your debt. If you have a bad rating or no credit at all, you will likely get stuck with a high-interest rate. If you have a long history of making your payments on time, you should be able to find a card with a low-interest rate.

It’s important to remember that changing your credit rating and locking in a lower interest rate will take time. Considering there’s only so much you can do to change your credit rating; you can reduce your credit card interest by paying off the outstanding balance as soon as possible. If your credit score has improved, call your current credit card company and see if they will lower your APR. Keep in mind that it's better to keep your old accounts than open new ones to "lock in" a lower rate

Before you sign on the dotted line, figure out how much you can afford to pay each month. Look for the minimum payment due at the end of each billing cycle and pay it in full to avoid incurring additional interest. The credit card company will identify a minimum monthly payment based on the total outstanding amount. This will either be expressed as a percentage of the current balance or a set monthly amount. You should be able to make this payment each month without fail. However, some credit cards may come with a grace period to shield consumers from extra fees.

If you can, try to pay off more than the minimum amount to pay off the loan faster. The more you pay upfront, the less interest you will accrue.

Carrying around high interest debt will only make it harder to get out of debt. If you have a high interest rate, consider looking for credit cards that offer balance transfers to lock in a lower interest rate so you can transfer your outstanding balance to the other card.

Some credit cards let you withdraw cash on credit, but credit cash advances often carry high-interest rates. Find out if the card issuer charges a higher rate for cash advances and avoid using this option to save on interest.

As you start making purchases with your credit card, avoid spending more than you can afford. It may be tempting to buy certain items on credit, but the longer you hold onto that debt, the more you will have to pay in interest.

Spend time comparing various types of credit cards from different lenders. Credit union interest rates are typically lower than banks, which will help you pay off the debt faster. If you are wondering how to consolidate your credit card debt, consult with a financial coach to learn more about debt repayment strategies and reach your financial goals.

Credit card interest FAQs

Interest is what you pay when you carry a balance from month to month. If you don't pay your entire statement balance by the due date, interest starts building on the remaining amount. Over time, that can make your debt more expensive—but knowing how it works is the first step toward staying ahead of it.

Most credit cards use something called the average daily balance method. That means they take what you owe each day of your billing cycle, average it, and then apply your annual percentage rate (APR) to that number. It sounds technical, but carrying a balance even for a few days can add up.

Paying your entire statement balance on time each month is the most effective way to avoid interest. Setting up automatic payments—even for the minimum—can help you stay on track. Pair that with a simple monthly budget, and you're taking tangible steps toward less stress and more control.

Making just the minimum might feel easier now, but it means more interest and a longer road to becoming debt-free. Even small extra payments can help you chip away at your balance faster and save money in the long run.

During a 0% APR promo, you won't pay interest on your balance—but once the promo ends, interest kicks in on whatever is left. Try to pay off as much as possible during that period to avoid surprises later.

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