Authorizes income tax addition and subtraction modifications for research and experimentation costs

HB 2457 updates Missouri's income tax rules to align more closely with federal tax calculations by adding and subtracting specific amounts from a taxpayer's federal adjusted gross income. The bill requires taxpayers to add back certain federal deductions, such as those for research and experimentation costs, interest expenses, and state tax refunds, while also allowing subtractions for items like interest on U.S. government bonds and combat zone pay. These adjustments primarily affect Missouri residents who itemize deductions on their federal returns or have income sources that differ between federal and state tax codes. The legislation aims to ensure that Missouri taxable income reflects the actual economic resources available to the taxpayer after accounting for federal tax benefits and limitations.