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Step 1
Determine your annual percentage rate for your credit card. This rate is usually listed at the bottom of your credit card statement. It is also located in the summary section that lists any payments you made the previous month, your total new charges for the current month and any late fees you owe.
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Step 2
Take this percentage and divide it by 12. As an example. If your annual percentage rate for your credit card is 18 percent, you would divide 18 by 12.
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Step 3
Calculate the result of dividing the annual percentage rate by 12. In the example from Step 2, the result is 1.5 percent. That is your monthly interest rate.
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Step 4
Find your total balance for the current month. This is typically located in two locations on your credit card bill. One is on the payment stub at the top of the bill, and the other is in the summary section where you found your APR for your credit card.
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Step 5
Convert the percentage you calculated to a decimal. This is done by moving the decimal point two places to the left and adding zeros after the decimal point and before the first number. In our example, the 1.5 percent would become a decimal of 0.015. Multiple this decimal times your current balance on your credit card. The result is your monthly interest payment based on the monthly percentage rate that was calculated from your credit card's APR.
