A method of amortization of premium or accrual of discount will be deemed "regularly employed" by a life insurance company if the method was consistently followed in prior taxable years, or if, in the case of a company which has never before made such adjustments, the company initiates in the first taxable year for which the adjustments are made a reasonable method of amortization of premium or accrual of discount and consistently follows such method thereafter. Ordinarily, a company regularly employs a method in accordance with the statute of some State, Territory, or the District of Columbia, in which it operates.
26 C.F.R. §1.818-3