Missouri Self-Employed — Schedule C, MO-1040 & MO-1040ES

Confirm the taxpayer is a full-year Missouri domiciliary (not a part-year or non-resident requiring MO-1040P/MO-NRI). Gather the prior-year return, federal extension status, and a list of all income sources. Flag any Kansas City or St. Louis residency that will trigger a separate 1% earnings tax filing.

Review the completed (or in-progress) federal Form 1040 and Schedule C. Verify that net self-employment profit is correctly computed — gross receipts minus allowable business expenses — and that the SE tax deduction and self-employed health insurance deduction are taken on Schedule 1. Missouri piggybacks on federal AGI, so accuracy here flows directly into the Missouri return.

Apply Missouri-specific additions and subtractions to federal AGI using Form MO-A. Key items for a self-employed filer: deduct federal income tax paid (capped at $5,000 single / $10,000 MFJ) per RSMo § 143.171, subtract Social Security benefits included in federal AGI (fully exempt), subtract 100% of net capital gains (effective TY 2025, RSMo § 143.022), add back any interest on non-Missouri state/municipal bonds, and subtract U.S. government bond interest.

Apply the standard deduction (or itemized if elected and larger), compute Missouri taxable income, and run the eight-bracket rate schedule (0% to 4.7%). Check eligibility for the Missouri Earned Income Tax Credit (mirrors federal EITC at 10%), the Property Tax Credit (Form MO-PTC for qualifying seniors/disabled), the Self-Employed Tax Credit (Schedule MO-SI), and the Credit for Taxes Paid to Other States (Form MO-CR) if the taxpayer had out-of-state income.

Missouri requires quarterly estimated payments when expected liability exceeds $100 (RSMo § 143.521). Compute the four installment amounts using current-year projected income, prepare MO-1040ES vouchers for each due date, and advise on safe-harbor options. Self-employed filers almost always owe estimates; underpayment triggers a penalty computed on Form MO-2210.