(a) The annual percentage rate applicable to any extension of consumer credit shall be determined in accordance with the regulations of the commissioner.

1. (1) In the case of any extension of credit other than an open-end-credit plan, as

   1. (A) that nominal annual percentage rate which will yield a sum equal to the amount of the finance charge when it is applied to the unpaid balances of the amount financed, calculated according to the actuarial method of allocating payments made on a debt between the amount financed and the amount of the finance charge, pursuant to which a payment is applied first to the accumulated finance charge and the balance is applied to the unpaid amount financed; or
   2. (B) the rate determined by any method prescribed by the commissioner as a method which materially simplifies computation while retaining reasonable accuracy as compared with the rate determined under subclause (A).
2. (2) In the case of an extension of credit under an open-end-credit plan, as the quotient, expressed as a percentage, of the total finance charge for the period to which it relates divided by the amount upon which the finance charge for that period is based, multiplied by the number of such periods in a year.