Mo. Rev. Stat. § 135.120
A taxpayer entitled to the credit allowed by section 135.110 may elect to defer the commencement of the ten-year period during which such credit is allowed to any taxable year not later than the third taxable year following the taxable year in which commencement of commercial operations at the new business facility occurs. The taxpayer shall perfect such election by notifying the director of economic development, by a written statement attached to the tax credit application for the taxable year in which commencement of commercial operations at the new business facility occurs, of the intention to make such election. The election shall be made during the taxable year immediately following the taxable year in which commencement of commercial operations occurs at such new business facility. Once such election has been perfected, the credit shall be allowed for the taxable year specified in such election and for each of the nine succeeding taxable years.
§ 135.120, RSMo