Montana Income Tax Calculator - MT State Tax Estimate

The montana income tax calculator estimates your annual Montana individual income tax from your federal adjusted gross income. Montana applies one flat state rate to your Montana taxable income, so the calculator takes your IRS Form 1040 AGI, subtracts the standard deduction for your filing status (Montana conforms to the federal standard deduction amount), and multiplies the remainder by the flat rate for the year you choose.

• • Plan a year-end tax payment: See what you owe before sending a fourth-quarter estimate to the Montana Department of Revenue.
• • Compare filing years: Compare 2024 and 2025 because the flat rate steps up from 4.7% to 4.9% under Montana's post-2023 reform.
• • Check a refund or balance due: Turn your expected liability into a refund or amount-due figure once you subtract Montana withholding.
• • Model a raise or bonus: Estimate how a higher AGI changes state tax now that the rate is flat rather than bracketed.

Because Montana no longer uses graduated brackets for individuals, the math is simpler than in many states, but the standard deduction still matters. The calculator focuses on the state piece only; it does not compute your federal tax.

Use the result as a planning estimate. Your actual Montana liability also depends on credits, other subtractions, and withholdings reported on your return. For per-paycheck withholding rather than an annual figure, the Montana paycheck calculator works from the same flat rate across each pay period.

If you are married and both spouses earn income, enter the combined federal AGI with the married filing jointly status, because Montana's standard deduction for that status is $31,500 in 2025, the largest of the four statuses.

If you want a per-paycheck view instead of an annual figure, the Montana paycheck calculator applies the same flat rate across each period.

The calculator follows the same steps the Montana return uses: start with federal AGI, subtract the larger of the standard deduction for your filing status or your itemized deductions, then apply the flat rate.

• federalAGI: Your federal adjusted gross income from IRS Form 1040.
• standardDeduction: Montana conforms to the federal standard deduction: $15,750 single, $23,625 head of household, $31,500 married filing jointly in 2025.
• itemizedDeductions: Your total itemized deductions, used only when they exceed the standard deduction.
• flatRate(year): The single Montana rate: 4.7% in 2024 and 4.9% in 2025.

Montana taxable income is never negative; if your deductions exceed AGI, the calculator reports zero taxable income and zero tax. The flat rate is applied to whole-dollar taxable income.

The same flat-rate logic appears in the federal income tax calculator for the federal side, but Montana uses a single rate while the federal system still uses brackets.

According to Montana Department of Revenue, Montana applies a single flat individual income tax rate rather than graduated brackets, with a 4.7% rate for 2024 and 4.9% for 2025.

For the federal side of the same return, the federal income tax calculator shows how brackets apply above the line where Montana starts.

Four ideas explain why the number moves the way it does.

These four ideas are enough to predict the result. If you want to compare a flat-rate neighbor, the Arizona income tax calculator shows how another flat-tax state handles the same AGI.

To compare how a flat-rate neighbor handles the same AGI, the Arizona income tax calculator runs the parallel estimate with Arizona's rate.

Follow these steps to get a clean estimate.

1. 1 Enter federal AGI: Pull the AGI figure from your IRS Form 1040, line 11, and enter it as Federal AGI.
2. 2 Pick filing status: Choose single, married filing jointly, married filing separately, or head of household; this sets the standard deduction.
3. 3 Add itemized deductions: Enter total itemized deductions; the calculator uses them only if they beat the standard deduction.
4. 4 Select the tax year: Choose 2024 or 2025 so the calculator uses the correct flat rate for that year.
5. 5 Read the outputs: Note Montana taxable income, state tax, and the effective state rate as a percent of AGI.
6. 6 Compare against withholding: Subtract Montana withholding already paid to see a refund or balance due.

A married couple with $100,000 AGI in 2025 and no itemized deductions enters those values, sees $68,500 taxable income (after the $31,500 standard deduction), and a $3,356.50 state tax at the 4.9% rate.

If you only have gross income and need the adjusted figure first, the AGI calculator builds the federal AGI the Montana estimate expects.

Running the estimate before you file helps you make specific decisions.

• • Avoid underpayment penalties: A year-end estimate shows whether your withholding covers the flat-rate liability so you can send a payment if needed.
• • Time a Roth conversion: Because the rate is flat, you can see the extra Montana tax from added income without bracket surprises.
• • Plan a bonus or raise: Model how a one-time amount changes state tax when every dollar is taxed at the same rate.
• • Decide standard versus itemized: The tool shows when itemized deductions pull taxable income below the standard-deduction path.
• • Track the rate change: Comparing 2024 and 2025 reveals the extra cost from Montana's step-up from 4.7% to 4.9%.
• • Coordinate with payroll: Share the annual figure with your employer's withholding so each paycheck comes out close.

The estimate is informational. Your filed return may differ after credits, other subtractions, and final withholdings are applied.

If you want to see the take-home impact of this annual tax, the gross-to-net calculator turns the same numbers into a per-period view.

Several inputs change the result; a few limits apply.

• • The calculator estimates individual income tax only; it excludes Montana credits, other subtractions, local earnings taxes, and federal tax.
• • Standard deduction and rate figures shown are the published amounts and may be updated by the Department of Revenue; confirm the current year's instructions before filing.

Montana also does not tax Social Security benefits, and the flat rate means planning is more predictable than in bracketed states. When the salary behind the AGI is easier to read as an annual figure, the annual income calculator annualizes the amount for you.

Because the rate is flat, a dollar of extra income above the deduction adds the same percentage of state tax whether it comes from a raise, a side job, or a retirement distribution. The main moving parts are therefore the standard deduction for your status, your itemized deductions, and the year's flat rate, not a bracket boundary.

As published by Internal Revenue Service, Montana filers begin with federal adjusted gross income reported on IRS Form 1040 before applying the state standard deduction (the federal amount) and any itemized deductions.

When the salary behind the AGI is prorated across the year, the annual income calculator annualizes it so the estimate lines up.