Average Daily Balance

The average daily balance is the average of the amounts owed on a credit card account across every day of a billing cycle, and it is the number an issuer multiplies by a periodic interest rate to produce the cycle's interest charge. Regulation Z, which implements the Truth in Lending Act, defines it at 12 CFR 1026.60(g)(1)(i) as a balance "figured by adding the outstanding balance (including new purchases and deducting payments and credits) for each day in the billing cycle, and then dividing by the number of days in the billing cycle." A parallel version at 1026.60(g)(1)(ii) excludes new purchases from the daily figures and is otherwise identical.

Two naming points prevent most of the confusion in this area. The method's formal category is the balance computation method, of which the average daily balance is one of five the regulation permits an issuer to identify by name, so "average daily balance" is a species and not a synonym for the whole idea. And the resulting dollar figure has a different name on the statement itself: 12 CFR 1026.7(b)(5) requires the amount to be disclosed "using the term Balance Subject to Interest Rate." A reader looking for "average daily balance" on a statement may well find that heading instead, with the method named beside it.

Regulation Z names five methods, and they are not equivalent. 12 CFR 1026.60(g) lists them: average daily balance including new purchases; average daily balance excluding new purchases; adjusted balance, "figured by deducting payments and credits made during the billing cycle from the outstanding balance at the beginning of the billing cycle"; previous balance, which is simply "the outstanding balance at the beginning of the billing cycle"; and daily balance, computed "for each day in the billing cycle" by "taking the beginning balance each day, adding any new purchases, and subtracting any payment and credits." On identical spending and an identical rate these produce materially different charges, because they differ in how much credit a payment made during the cycle receives. The adjusted balance method deducts such payments in full, which makes it the most favorable of the five to the cardholder. The previous balance method deducts none of them, though it also ignores new purchases, so which of the remaining four costs the most depends on how much was spent during the cycle and when.

Naming a method is not the same as pinning down the arithmetic, and the regulation says so in its own preamble. 12 CFR 1026.60(g) opens: "The following methods may be described by name. Methods that differ due to variations such as the allocation of payments, whether the finance charge begins to accrue on the transaction date or the date of posting the transaction, the existence or length of a grace period, and whether the balance is adjusted by charges such as late payment fees, annual fees and unpaid finance charges do not constitute separate balance computation methods." So two cards can both truthfully disclose "average daily balance including new purchases" and still charge different amounts on the same transactions. The name narrows the possibilities; the agreement settles them.

The other half of the calculation is the rate, and it has its own disclosure rule. Interest is the balance multiplied by a periodic rate, and 12 CFR 1026.6(b)(4)(i)(A) requires an account's opening disclosures to give "the rate, expressed as a periodic rate and a corresponding annual percentage rate," with paragraph (D) separately requiring "an explanation of the method used to determine the balance to which the rate is applied." Where an issuer computes interest daily, that periodic rate is a daily one. The relationship between the two figures is fixed by 12 CFR 1026.14(b), which provides that the annual percentage rate "shall be computed by multiplying each periodic rate by the number of periods in a year." A card quoting an annual percentage rate and a daily periodic rate is therefore quoting one number in two forms, and the daily rate is the annual one divided back down by the days in the year.

Two of the five named methods are arithmetically the same, which is worth knowing before comparing cards. Summing a rate applied to each day's balance gives the same total as applying that rate to the average of those balances and multiplying by the number of days, because both are the rate times the sum of the daily balances. So the daily balance method and the average daily balance method including new purchases coincide on an account with one rate and no interest added inside the cycle. The differences that actually change a bill are the ones between those two and the adjusted, previous and purchase-excluding methods, plus the agreement-level variations the regulation's preamble lists.

What the statement is required to tell you, and the escape hatch issuers may use. 12 CFR 1026.7(b)(5) requires the periodic statement to give the amount of the balance a periodic rate was applied to "and an explanation of how that balance was determined, using the term Balance Subject to Interest Rate." It then permits a substitution: an issuer using one of the 1026.60(g) methods may instead "identify the name of the balance computation method and provide a toll-free telephone number where consumers may obtain from the creditor more information about the balance computation method and how resulting interest charges were determined." An issuer using a method not on the list "shall provide a brief explanation of the method used." The same paragraph adds a requirement aimed squarely at the less favorable methods: "when a balance is determined without first deducting all credits and payments made during the billing cycle, the fact and the amount of the credits and payments shall be disclosed." The practical reading is that the statement always names either the method or the arithmetic, so the computation behind an interest charge is checkable rather than opaque.

None of this applies to a statement paid in full. The method decides what a carried balance costs. An account whose statement balance is paid by the due date is inside the interest-free window, and no periodic-rate interest is charged on those purchases at all, which is a separate mechanism with its own rules and its own page.

The same two methods govern the deposit side, in a different regulation. 12 CFR 1030.7(a)(1), part of Regulation DD, requires a bank to calculate interest on a deposit account "by use of either the daily balance method or the average daily balance method." The arithmetic is the same and the direction is reversed: on a card the figure decides what a borrower pays, and on a savings account it decides what a depositor earns.

Take the amount owed at the end of each day of the billing cycle, add those daily amounts together, and divide by the number of days in the cycle. Multiply the result by the periodic rate and by the number of days, and that is the cycle's interest charge on that balance.

A hypothetical example, with a hypothetical rate. A card has a 30-day billing cycle and an annual percentage rate of 21.99 percent, and the account is already carrying a balance, so purchases accrue interest from posting rather than sitting inside a grace period. The balance is $2,000 for the first 10 days. A $500 payment posts on day 11, leaving $1,500 for days 11 through 20. A $300 purchase posts on day 21, taking the balance to $1,800 for days 21 through 30.

The daily balances add up to (10 × $2,000) + (10 × $1,500) + (10 × $1,800) = $20,000 + $15,000 + $18,000 = $53,000. Divided by 30 days, the average daily balance is $1,766.67. The daily periodic rate is 21.99% ÷ 365 = 0.0602466 percent a day. Interest for the cycle is $1,766.67 × 0.000602466 × 30 = $31.93.

Now the same cycle under the other named methods, which is the whole point of the disclosure. Under the previous balance method the rate is applied to the $2,000 the cycle opened with, ignoring both the payment and the purchase: $2,000 × 0.000602466 × 30 = $36.15. Under the adjusted balance method the $500 payment is deducted from the opening balance and the purchase is ignored: $1,500 × 0.000602466 × 30 = $27.11. Under average daily balance excluding new purchases the daily figures omit the $300 purchase, giving (10 × $2,000) + (20 × $1,500) = $50,000, an average of $1,666.67, and interest of $30.12.

Same spending, same payment, same rate, same 30 days: $36.15, $31.93, $30.12 or $27.11, depending only on which method the agreement specifies. The spread between the highest and lowest is about a third of the smaller charge. A shortcut worth knowing for checking a statement: because the average is divided by the days and then multiplied back by them, the interest also equals the summed daily balances times the daily rate, so $53,000 × 0.000602466 gives the same $31.93 without computing the average at all.

Pros

• Charges interest for the time a balance was actually outstanding, so a payment made early in the cycle reduces the bill rather than being ignored until the due date.
• Codified and named, so a cardholder can look up exactly what the disclosed method means instead of taking the issuer's arithmetic on trust.
• Required to be disclosed both at account opening and on every periodic statement, which makes an interest charge checkable by hand.
• Broadly self-correcting for irregular spending: the average reflects the real pattern of the month rather than a single snapshot.

Cons

• Including new purchases in the daily figures means a purchase made early in the cycle raises the balance interest is charged on for the rest of it.
• The disclosed name does not fully determine the charge, because the regulation treats payment allocation, accrual start date and fee adjustments as variations rather than separate methods.
• Comparing two cards on the method alone is unreliable, since the rate, the fee schedule and the agreement's own variations all move the answer.
• The arithmetic is tedious to verify without the daily balances, and a statement is only required to give the resulting figure plus either an explanation or a phone number.
• It is easy to misread the average as a balance you owe. It is a computed input, not an amount due.