Credit Card Interest Calculator for Statement Charges
This credit card interest calculator estimates statement charges from average daily balance, APR divided by 365, and billing-cycle days. It checks disclosed figures but does not reproduce every issuer method.
Average daily balance × APR ÷ 365 × cycle days
Enter the average daily balance and APR shown for one balance category.
Build the average before using the calculator
The average daily balance is a weighted average, not the midpoint between opening and closing balances. Reconstruct it from the dates on which the applicable balance changed.
- Start with the category balance.Use the opening purchase, transfer, or cash-advance balance for the first day of the cycle.
- Apply posted activity.Change the balance on the date specified by the issuer's method, keeping purchases and payments in their correct APR category.
- Count unchanged days.Multiply each balance by the number of days it remained in effect.
- Divide once.Add the balance-day products and divide by the full cycle day count. Avoid rounding each interval too early.
Rounding check: Keep the daily rate and balance-day total at full available precision until the final currency result. If the statement differs by a few cents, test the issuer's stated denominator and rounding sequence before changing transaction dates.
How to obtain the right average daily balance
List the opening balance, apply each posted transaction on its effective date, count the days each balance remained, and divide the sum of daily balances by the cycle length.
Do not use the closing balance as a substitute
The closing balance describes one point in time. Interest under an average daily balance method depends on the path taken through the cycle.
Match the APR category
A purchase APR does not describe a cash advance or a balance transfer when the statement lists a different rate.
Interest estimate example
An average daily balance of $1,500 at 24% APR over a 30-day cycle produces an estimate of $29.59 using a 365-day denominator.
| Calculation step | Worked value |
|---|---|
| Daily periodic rate | 24% ÷ 365 = about 0.06575% |
| Daily interest | $1,500 × 0.0006575 = about $0.99 |
| Cycle estimate | About $0.99 × 30 = $29.59 |
Why an issuer charge can be different
Your agreement controls the denominator, compounding, transaction dates, grace period, rounding, and treatment of new activity. Build the source schedule with the average daily balance reference before comparing the result.
Grace period
Qualifying purchases may avoid interest when the required balance is paid under the agreement.
Residual interest
Interest can accrue between a statement closing date and the date a payment reaches the account.
Multiple APRs
Calculate each balance category separately before comparing their sum with the statement.