Find your card’s APR
Divide the APR by 365 to get the daily periodic rate
Check your statement balance or average daily balance
Multiply the balance by the daily periodic rate
Multiply that result by the number of days in the billing cycle
Subtract any grace period effect if you paid the full statement balance before the due date
Add interest from purchases, cash advances, or balance transfers separately if needed
Include any fees that are subject to interest if your card terms say so
Use the exact method in your card agreement if it differs from the simple daily calculation
Compare the result to your statement’s finance charge to verify it