Individuals must adopt the calendar year, or a fiscal year if he/she maintains their books and records on the basis of the adopted fiscal year.
However, a newly married couple can adopt the accounting period of the other spouse without getting previous approval.
Usually partnerships, S Corporations, and Personal Service Corporations (PSCs) must use a required tax year under the Internal Revenue Code and Income Tax Regulations. However, they may use another tax year if approved by the IRS or made an election under section 444.