How to Complete Missouri Form MO-A: Adjustments, Deductions, Pensions

Missouri Form MO-A is the individual income tax adjustments schedule you attach to your MO-1040 whenever you need to change your federal adjusted gross income for Missouri purposes, itemize deductions on your state return, or claim a pension or Social Security exemption.¹ The form has three parts, and you only fill in the parts that apply to you. For the 2025 tax year, Form MO-A is due with your MO-1040 by April 15, 2026.

Do You Actually Need Form MO-A

Skip the form if you are taking the Missouri standard deduction and none of the additions or subtractions below apply. Otherwise, you need it. File Form MO-A if any of these fit your situation:

You received interest on bonds issued by another state, took a non-qualified 529 withdrawal, or need to add back a positive Missouri adjustment reported on a K-1.
You have interest on U.S. government obligations, military retirement pay, a Missouri refund included in federal income, or contributions to a Missouri MOST 529 or ABLE account.
You want to claim the pension exemption, the Social Security exemption, or both.
You want to itemize on your Missouri return instead of taking the standard deduction.

The statutory list of additions and subtractions that turn federal AGI into Missouri AGI lives in Missouri Revised Statutes Section 143.121.²

What to Have In Front of You

Every line on Form MO-A traces back to something on your federal return or a supporting document. Pull these together first:

Your completed federal Form 1040. A copy has to be attached to your Missouri return anyway.
W-2s and 1099s, including 1099-R for retirement distributions and SSA-1099 for Social Security.
Federal Schedule B or any K-1 if you have out-of-state municipal bond interest or partnership, S corporation, or fiduciary adjustments.
Federal Schedule A, only if you plan to itemize on the state return.
Year-end statements for any 529 or ABLE contributions.

The current form and its line-by-line instructions are in the MO-1040 instruction booklet on the Department of Revenue website.³

Part 1: Additions and Subtractions to Federal AGI

Part 1 recalculates your income for Missouri. Additions come first and increase your Missouri income; subtractions come next and reduce it. The net figure carries over to Form MO-1040.¹

Common Additions

Line 1 is for interest on bonds issued by another state or its political subdivisions. That income is tax-free federally but taxable in Missouri. Reduce it by any related management or trustee fees if those fees exceed $500.³ Missouri-issued bond interest stays exempt.

Line 2 collects several less common items, including positive Missouri adjustments reported to you by a partnership, S corporation, or fiduciary. Attach a copy of any notification you received. Line 3 is for non-qualified 529 plan withdrawals: the previously deducted contributions plus the earnings portion of the distribution get added back.

Common Subtractions

The subtractions section starts at Line 8. The ones most filers use:

Line 8, interest on U.S. government obligations such as Treasury bonds, notes, and bills. Attach your 1099s or a supporting list.
Line 9, a Missouri income tax refund from a prior year that was included in your federal income. Missouri does not tax its own refund a second time.²
Line 10, military retirement benefits. All military retirement pay qualifies; use the worksheet in the MO-1040 booklet.
Line 12, contributions to a qualified 529 education savings plan, up to $8,000 per person or $16,000 for married couples filing combined. Rollovers from another 529 do not qualify.⁴
Line 15, contributions to an ABLE account, using the same $8,000 single and $16,000 combined caps.⁵
Line 17, the business income deduction. A worksheet in the MO-1040 instructions walks through the calculation.

Total your additions and subtractions separately, then carry the net figure to your MO-1040 as instructed.

Part 2: Missouri Itemized Deductions

Only fill in Part 2 if itemizing beats the Missouri standard deduction. For 2025 the standard deduction is $15,750 for single or married filing separately, $31,500 for married filing combined or qualifying widow(er), and $23,625 for head of household.⁶

Start with your total federal itemized deductions from Schedule A. Missouri then requires two adjustments. First, subtract the portion representing state and local income taxes claimed on the federal return. Missouri does not let you deduct state income taxes paid to Missouri or any other state. Second, you can add back the employee share of Social Security and Medicare taxes (FICA), railroad retirement taxes, and self-employment taxes paid during the year, to the extent they were not already deducted in arriving at federal AGI.

There is one additional line worth knowing about. If you created and donated a literary, musical, scholarly, or artistic work to a tax-exempt nonprofit, you can add the fair market value of the work to your Missouri itemized deductions. You have to attach a written appraisal made within a year of the donation by someone who is neither you nor the receiving organization.

Compare the resulting Missouri itemized total to the standard deduction for your filing status. Use the larger of the two on your MO-1040.

Part 3: Pension and Social Security Exemptions

Part 3 has three sections. You can claim more than one, but they interact.

Section C: Social Security

Starting with the 2024 tax year, Missouri exempts 100% of Social Security benefits for taxpayers age 62 or older by December 31 of the tax year. Social Security disability benefits are fully exempt at any age.⁷ Enter the Social Security income included in your federal AGI and subtract the full amount. Check the “62 and older” box on page 1 of the MO-1040 if you are claiming the age-based version.

Section A: Public Pensions

Pensions from federal, state, or local government sources are subtractable up to the maximum Social Security benefit for the year. For 2026 that cap is $48,967.⁷ If you also claim the Social Security exemption, the public pension subtraction is reduced dollar for dollar by whatever Social Security amount you already subtracted. The MO-1040 booklet includes the worksheet.

Section B: Private Pensions

Private pension income, from IRAs, 401(k) plans, and corporate pensions, has a smaller cap of $6,000 per taxpayer. The full amount is available only if your Missouri AGI is at or below the threshold for your filing status:

$25,000 for single, head of household, or qualifying widow(er)
$32,000 for married filing combined
$16,000 for married filing separately⁷

Above the threshold, the exemption shrinks by one dollar for every dollar over. A single filer with $31,000 of Missouri AGI, for example, gets nothing.

How to Submit It

Form MO-A never goes in on its own. Attach it directly behind your MO-1040. If you are mailing, the address depends on whether you owe:

Balance due: Missouri Department of Revenue, P.O. Box 329, Jefferson City, MO 65105-0329
Refund or zero balance: Missouri Department of Revenue, P.O. Box 500, Jefferson City, MO 65105-0500⁸

If you e-file through approved tax software, Form MO-A is transmitted as part of the MO-1040 automatically.⁹

Fixing a Mistake After You File

Missouri has no separate amendment form. To correct an error, fill out a new MO-1040 for that tax year, check the amended return box, and attach a corrected Form MO-A.¹⁰ If the change flows from a federal correction, include the amended federal return too. Common triggers are a missed 529 subtraction, a miscalculated pension exemption, or realizing itemizing would have been better than the standard deduction.

Keep Your Records at Least Three Years

Missouri requires taxpayers to keep records for at least three years from the date an original, additional, or amended return is filed.¹¹ That covers your copy of Form MO-A, the MO-1040, W-2s, 1099s, and any worksheets used for pension or Social Security calculations. If the Department of Revenue questions a subtraction or deduction later, those documents are your proof.

1
Missouri Department of Revenue. Missouri Form MO-A – 2025 Individual Income Tax Adjustments
2
Missouri Revisor of Statutes. Missouri Code 143.121 – Missouri Adjusted Gross Income
3
Missouri Department of Revenue. Individual Income Tax Long Form MO-1040 Instructions
4
MOST 529. Tax Advantages
5
Missouri Department of Revenue. Achieving a Better Life Experience (ABLE) FAQs
6
Missouri Department of Revenue. 2025 Individual Income Tax Year Changes
7
Missouri Department of Revenue. Pension FAQs
8
Missouri Department of Revenue. Missouri Department of Revenue to Begin Accepting E-Filed State Tax Returns Jan. 27
9
Missouri Department of Revenue. Individual Income Tax Electronic Filing
10
Missouri Department of Revenue. How Do I Correct a Mistake I Made on My Electronic or Paper Tax Filing
11
Missouri Department of Revenue. 12 CSR 10-101.800 – Record Keeping and Record Retention