Average daily balance is the mean of daily account balances during a billing cycle, commonly used with a periodic rate to calculate credit-card interest.
The average daily balance (ADB) is the sum of an account’s balance for each day in a billing cycle divided by the number of days in that cycle. Many credit-card issuers use it with a daily periodic rate to calculate interest for purchases, cash advances, balance transfers, or other balance categories.
The card agreement and statement control the calculation. Transaction posting, payments, credits, fees, compounding, grace periods, and separate APR categories can all change the result.
For a cycle with (D) days:
A simplified noncompounding interest estimate is:
If the agreement uses 365 days:
Some agreements use another divisor or compound interest daily, so the disclosed method must replace this simplified assumption.
Assume a 30-day billing cycle with one purchase-balance category:
| Days | Daily balance | Days at balance | Balance-days |
|---|---|---|---|
| 1-10 | $1,000 | 10 | $10,000 |
| 11-20 | $600 after a $400 payment | 10 | $6,000 |
| 21-30 | $900 after a $300 purchase | 10 | $9,000 |
| Total | 30 | $25,000 |
The average daily balance is:
If the APR is 24%, the agreement uses a 365-day divisor, no grace period applies, and the simplified noncompounding method is appropriate:
This is an educational estimate, not a reconstructed statement. Rounding, posting dates, daily compounding, fees, multiple APRs, and later adjustments can change the issuer’s figure.
Suppose the $400 payment in the example is credited on day 21 rather than day 11. The balance would remain $1,000 for 20 days before falling, creating more balance-days and a higher average. The payment amount is unchanged, but it reduces the balance for fewer days.
Under U.S. Regulation Z, a creditor generally must credit a conforming payment as of the date of receipt, subject to specified rules. The date a consumer initiates a transfer may differ from the issuer’s receipt or crediting date. Check the statement’s payment instructions and cutoff time.
Regulation Z defines named balance-computation methods that issuers can disclose:
| Method | Simplified treatment |
|---|---|
| Average daily balance, including new purchases | Adds new purchases and subtracts payments and credits in daily balances |
| Average daily balance, excluding new purchases | Excludes new purchases but subtracts payments and credits |
| Adjusted balance | Starts with the beginning balance and subtracts cycle payments and credits |
| Previous balance | Uses the outstanding balance at the beginning of the cycle |
| Daily balance | Applies the periodic rate to each day’s computed balance |
These names do not capture every contractual detail. An agreement can separately address when transactions enter the balance, how fees are treated, whether unpaid interest compounds, and how payments are allocated.
A card can have different APRs for purchases, cash advances, balance transfers, penalty pricing, or promotions. The issuer may calculate separate daily balances and interest charges for each category.
For example, a card could show:
Adding all three balances and applying one rate would be wrong. Review the statement’s Interest Charge Calculation section, each balance subject to interest, the corresponding APR, and the disclosed method.
Average daily balance is a calculation method, not a statement that interest must be charged. A card’s purchase grace period may allow a consumer to avoid purchase interest by paying the required balance in full by the due date, subject to the agreement. Cash advances and some other balance categories commonly follow different terms.
Once a purchase grace period is lost, restoring it may require satisfying conditions over one or more cycles. Paying only the Minimum Monthly Payment generally does not preserve a grace period on a carried purchase balance.
This page provides general U.S.-focused financial education, not a legal conclusion or individualized debt-repayment recommendation.