Mo. Rev. Stat. § 143.271: Period for computation of taxable income.

1. For purposes of taxes imposed by sections 143.011 to 143.996, a taxpayer's taxable year shall be the same as his taxable year for federal income tax purposes.

2. If a taxpayer's taxable year is changed for federal income tax purposes, his taxable year for purposes of the tax imposed by sections 143.011 to 143.996 shall be similarly changed. If a change in taxable year results in a taxable period of less than twelve months, the deductions allowed by sections 143.011 to 143.996 shall be prorated under regulations prescribed by the director of revenue.