How a Missouri paycheck works
Missouri withholding annualises the wage, subtracts a standard deduction that matches the filing status on Form MO W-4, then runs the remainder through a graduated table of narrow bands before rounding the result to whole dollars. The bands are unusually tight, so most employees reach the top rate on a modest salary and the tax behaves almost like a flat rate above that point.
Federal income tax withholding
Federal withholding annualises the wage, subtracts the standard deduction that matches the filing status on Form W-4 Step 1, applies the graduated schedule for that status, and deducts the dependent credit from Step 3. This page models a W-4 with Steps 2 and 4 left blank: one job, no spouse income, no other income, no extra withholding. Above the income limit for the status, the dependent credit tapers by a set amount for every thousand dollars of excess rather than disappearing at a cliff.
Social Security and Medicare
Social Security applies a flat rate to wages up to an annual ceiling that is re-indexed each year, so it stops partway through the year for a high earner. Medicare applies to every dollar, and above a fixed wage threshold the employer withholds the Additional Medicare tax on the excess, with no employer match and no regard for filing status.
Missouri no longer deducts your federal tax
Missouri used to be one of a small group of states that let you subtract federal income tax before working out the state tax, which made state withholding depend on your federal withholding. That deduction is gone from the withholding formula. The practical effect is that the state line no longer moves when something changes your federal tax alone, and the calculation is far easier to check by hand.
Form MO W-4 and the standard deduction
Missouri matches its standard deduction to the federal one for the same status, so the figures are familiar. Single, married filing separately, and married where both spouses work all use the same amount. Head of household gets a larger one.
The interesting case is a married couple with one income. Missouri does not treat it as a separate filing status; it is a check box on the first line of Form MO W-4 saying the spouse does not work. Tick it and the deduction doubles, which is why selecting it here can move the state line by several hundred dollars a year. Leave it unticked, as a couple who both work should, and withholding uses the single amount on each payroll.
Narrow bands and the printed table
The percentage table steps up through eight bands, each about the same small width, from a nil band at the bottom to the top rate. Because the bands are so narrow, taxable income above a fairly low figure lands in the top band, and the tax from there on is the top rate on the excess plus a fixed cumulative amount.
That cumulative amount is worth a note for anyone reproducing the calculation. Missouri prints it rounded to whole dollars at each step rather than carrying the exact arithmetic forward, so the published figures are a few tens of cents away from an exact accumulation. This page uses the numbers as printed, because those are the ones an employer applies.
Local income tax
Kansas City and St. Louis each charge an earnings tax on wages earned in the city, and it applies whether or not you live there. It is not included in this figure. Nowhere else in Missouri has a local income tax, so for most of the state the payroll deductions shown here are the whole picture.
What the employer pays on top
The employer matches Social Security and Medicare and pays federal unemployment tax at its net rate. Missouri unemployment insurance is charged to the employer at a rate set from its own claims record on a state wage base, so it is left out. There is no employee-side state levy in Missouri.
What this calculator assumes
The figure models a salaried employee paid evenly across the year with a standard Form W-4 and Form MO W-4, and no pre-tax deductions. It leaves out:
- Pre-tax contributions such as a 401(k), health premiums, HSA or flexible spending accounts, which reduce the wages subject to income tax and often to FICA.
- Extra withholding requested on the federal or state certificate, and the W-4 Step 2 and Step 4 adjustments.
- Bonuses and other supplemental wages, which may be withheld at a flat supplemental rate.
- The Kansas City and St. Louis earnings taxes.
- Employer-side state unemployment insurance, which is priced per employer, and any federal unemployment credit reduction.
- Employees outside the normal Social Security system, such as some public-sector staff and certain visa holders.
Withholding versus your final tax bill
Withholding is a prepayment. The annual returns, federal and state, replace these standard assumptions with your real situation: itemised deductions, other income, and credits payroll knows nothing about. One job usually produces a refund; two jobs, a working spouse or investment income often produce a balance due.