A.R.S. § 43-931: Change of accounting period; computation of income; due date of return

If a separate return is made under section 443 of the internal revenue code on account of a change in the accounting period, and in all other cases in which a separate return is required or allowed by treasury regulations to be made for a fractional part of a year, the income shall be computed on the basis of the period for which the separate return is made. Except for partnership and S corporation returns, the due date of the separate return for the period is the fifteenth day of the fourth month following the close of that period unless the short period return is due to a change in ownership of a corporation, in which case the due date shall be determined pursuant to treasury regulations. For a partnership or S corporation, the due date of the separate return for the period is the fifteenth day of the third month following the close of that period.