(1) With respect to a consumer credit sale made pursuant to a revolving charge account, the parties to the sale may contract for the payment by the buyer of a credit service charge not exceeding that permitted in this section but, if they do not so contract in writing no charge shall be made.

(2) A charge may be made in each billing cycle which is a percentage of an amount no greater than:

(a) the average daily balance of the account,

(b) the unpaid balance of the account on the same day of the billing cycle, or

(c) the median amount within a specified range within which the average daily balance of the account or the unpaid balance of the account on the same day of the billing cycle is included. A charge may be made pursuant to this paragraph only if the seller, subject to classifications and differentiations he may reasonably establish, makes the same charge on all balances within the specified range and if the percentage when applied to the median amount within the range does not produce a charge exceeding the charge resulting from applying that percentage to the lowest amount within the range by more than eight percent of the charge on the median amount.

(3) If the billing cycle is monthly, the charge may not exceed that authorized by § 37-2-201 on the amount specified in subsection (2). If the billing cycle is not monthly, the maximum charge is that percentage which bears the same relation to the applicable monthly percentage as the number of days in the billing cycle bears to thirty. For the purposes of this section, a variation of not more than four days from month to month is the same day of the billing cycle.

(4) Notwithstanding subsection (3), if there is an unpaid balance on the same date as of which the credit service charge is applied, the seller may contract for and receive a charge not exceeding fifty cents if the billing cycle is monthly or longer, or the pro rata part of fifty cents which bears the same relation to fifty cents as the number of days in the billing cycle bears to thirty if the billing cycle is shorter than monthly.

(5) Notwithstanding subsection (3), and except for subsection (4), no less than forty percent of any scheduled minimum payment for that billing cycle must be applied to principal reduction in that billing cycle, provided, however, that failure to apply the forty percent of a scheduled minimum payment is not a violation of this subsection when the consumer has agreed in writing to a promotion offered by the creditor that includes deferred payments, deferred or waived finance charges, a combination thereof, or other special financing terms. Such exception shall only apply during the period of time necessary to comply with the provisions of the promotional agreement identified in writing to the customer.