26 U.S.C. § 1378: Taxable year of S corporation

(a) General ruleFor purposes of this subtitle, the taxable year of an S corporation shall be a permitted year. (b) Permitted year definedFor purposes of this section, the term “permitted year” means a taxable year which—(1) is a year ending December 31, or (2) is any other accounting period for which the corporation establishes a business purpose to the satisfaction of the Secretary. For purposes of paragraph (2), any deferral of income to shareholders shall not be treated as a business purpose.