Transaction charge imposed.
(3) Transaction charge imposed. If the finance charge imposed during the billing cycle is or includes a charge relating to a specific transaction during the billing cycle (even if the total finance charge also includes any other minimum, fixed, or other charge not due to the application of a periodic rate), by dividing the total finance charge imposed during the billing cycle by the total of all balances and other amounts on which a finance charge was imposed during the billing cycle without duplication, and multiplying the quotient (expressed as a percentage) by the number of billing cycles in a year, except that the annual percentage rate shall not be less than the largest rate determined by multiplying each periodic rate imposed during the billing cycle by the number of periods in a year. Where the finance charge imposed during the billing cycle is or includes a loan fee, points, or similar charge that relates to the opening, renewing, or continuing an account, the amount of such charge shall not be included in the calculation of the annual percentage rate. See appendix F to this part regarding determination of the denominator of the fraction under this paragraph.
12 CFR § 1026.14
General rule. The annual percentage rate is a measure of the cost of credit, expressed as a yearly rate. An annual percentage rate shall be considered accurate if it is not more than 1/8th of 1 percentage point above or below the annual percentage rate determined in accordance with this section. An error in disclosure of the annual percentage rate or finance charge shall not, in itself, be considered a violation of this part if:
(1) The error resulted from a corresponding error in a calculation tool used in good faith by the creditor; and
(2) Upon discovery of the error, the creditor promptly discontinues use of that calculation tool for disclosure purposes, and notifies the Bureau in writing of the error in the calculation tool.