Taxable income is computed on the basis of a period of time called a tax year. A tax year generally is the annual period on the basis of which the taxpayer regularly computes income in keeping its books and records. The annual period is usually a calendar year or a fiscal year. A calendar year is a period of twelve (12) months ending on December 31. A fiscal year is a period of Twelve (12) months ending on the last day of any month other than December.

A taxpayer must calculate income using the same tax year as that used on the federal income tax return. A change of the tax year must be approved by the Internal Revenue Service and a copy of the approval letter must be attached to the Arkansas income tax return