Credit Card Interest Calculator
Estimate the interest a credit card charges in a billing cycle from its APR and your average daily balance.
About the Credit Card Interest Calculator
Most US card issuers use the average daily balance method: the APR is divided by 365 (or 360) to get a daily periodic rate, which is applied to your average balance for each day in the cycle. Paying the full statement balance by the due date usually avoids interest on purchases.
The formula
Interest = average daily balance × (APR ÷ 365) × days in cycle
Worked example
Example: Interest this cycle = $67.81
- Inputs: Average daily balance: $3,300; APR: 25%; Days in the billing cycle: 30 days.
- Formula: Interest = average daily balance × (APR ÷ 365) × days in cycle
- Result: Interest this cycle = $67.81
Questions people ask
Why was I charged interest after paying in full?
If you didn't pay in full the previous month, interest can accrue until the payment posts (trailing interest).
Is it 365 or 360?
Check your card agreement; some issuers use 360.