Find your card’s annual percentage rate (APR)
Divide the APR by 365 to get the daily periodic rate
Multiply your average daily balance by the daily periodic rate
Multiply that result by the number of days in the billing cycle
If your card uses monthly compounding, divide the APR by 12 instead
Add any fees that are subject to interest if applicable
Subtract any payments made before the statement closing date
Use the statement balance if your card does not use a grace period
Use the average daily balance if your card calculates interest that way
Check your credit card statement for the exact interest calculation method
Use an online credit card interest calculator for a quick estimate