Mo. Rev. Stat. § 143.125
2. For the taxable year beginning on or after January 1, 2007, any taxpayer shall be allowed to subtract from the taxpayer's Missouri adjusted gross income to determine Missouri taxable income a maximum of an amount equal to twenty percent of the amount of any benefits received by the taxpayer and that are included in federal adjusted gross income under Section 86 of the Internal Revenue Code of 1986, as amended. For the taxable year beginning on or after January 1, 2008, any taxpayer shall be allowed to subtract from the taxpayer's Missouri adjusted gross income to determine Missouri taxable income a maximum of an amount equal to thirty-five percent of the amount of any benefits received by the taxpayer and that are included in federal adjusted gross income under Section 86 of the Internal Revenue Code of 1986, as amended. For the taxable year beginning on or after January 1, 2009, any taxpayer shall be allowed to subtract from the taxpayer's Missouri adjusted gross income to determine Missouri taxable income a maximum of an amount equal to fifty percent of the amount of any benefits received by the taxpayer and that are included in federal adjusted gross income under Section 86 of the Internal Revenue Code of 1986, as amended. For the taxable year beginning on or after January 1, 2010, any taxpayer shall be allowed to subtract from the taxpayer's Missouri adjusted gross income to determine Missouri taxable income a maximum of an amount equal to sixty-five percent of the amount of any benefits received by the taxpayer and that are included in federal adjusted gross income under Section 86 of the Internal Revenue Code of 1986, as amended. For the taxable year beginning on or after January 1, 2011, any taxpayer shall be allowed to subtract from the taxpayer's Missouri adjusted gross income to determine Missouri taxable income a maximum of an amount equal to eighty percent of the amount of any benefits received by the taxpayer and that are included in federal adjusted gross income under Section 86 of the Internal Revenue Code of 1986, as amended. For all taxable years beginning on or after January 1, 2012, any taxpayer shall be allowed to subtract from the taxpayer's Missouri adjusted gross income to determine Missouri taxable income a maximum of an amount equal to one hundred percent of the amount of any benefits received by the taxpayer and that are included in federal adjusted gross income under Section 86 of the Internal Revenue Code of 1986, as amended. A taxpayer shall be entitled to the maximum exemption provided by this subsection:
(L. 2007 H.B. 444, et al.)