Which income does this calculator use?

It uses Montana taxable income as the base. In tax year 2024 and later, Montana’s tax starts from a simplified base closely aligned with federal taxable income with state adjustments. Consult MT DOR instructions if you are unsure of your taxable income.

Does it include credits and surcharges?

No. It computes tax before nonrefundable/refundable credits or other additions. Credits vary by taxpayer—apply them after this result.

Are 2025 thresholds indexed for inflation?

Montana law provides for inflation adjustments. We preload current published values and allow manual overrides in the Advanced settings if new figures are released.

Is Head of Household supported?

Yes. Thresholds scale relative to Single. Verify your filing status per Montana DOR definitions.

How accurate is the result?

When the correct taxable income and current-year parameters are used, the result matches Montana’s two-rate formula before credits. Always verify with official instructions.

Can I export or copy results?

Yes. You can copy the breakdown from the Results area. Printing to PDF preserves the structure.

The tool was developed by Ugo Candido with UX/A11y-first design and reviewed for accuracy by the CalcDomain editorial team.

Montana State Income Tax Calculator | 2024–2025 Accurate & Accessible Tool

This Montana income tax calculator is designed for residents, part‑year residents, and nonresidents with Montana‑source income who want a fast, accurate estimate of state income tax before credits. It provides a transparent bracket breakdown, effective and marginal rates, and complies with WCAG 2.1 AA for assistive technologies.

Data Source and Methodology

Authoritative Data Sources

Montana Department of Revenue — Montana Tax Simplification Resource Hub (Tax Years 2024+). Latest guidance and forms: revenue.mt.gov/montana-tax-simplification-resource-hub (accessed 2025).
Montana Code Annotated — Individual Income Tax Rates and Brackets (e.g., MCA §15-30-2103 as amended by SB 399). Official statutory definitions: MCA §15-30-2103.

All calculations are strictly based on the formulas and data provided by these sources.

Important: This tool computes tax before nonrefundable and refundable credits. Montana adjusts bracket parameters for inflation; defaults are preloaded for the selected year and can be overridden in “Advanced” if new figures are announced.

The Formula Explained

Let taxable income be T, lower rate r_1, higher rate r_2, and threshold b. Montana’s two-rate structure is:

Tax components:

Lower-bracket portion: $ \text{LB} = \min(T,\, b)\times r_1 $

Upper-bracket portion: $ \text{UB} = \max(T - b,\, 0)\times r_2 $

Total tax before credits:

$ \text{Tax} = \text{LB} + \text{UB} $

Marginal rate:

$ \text{MR} = \begin{cases} r_1, & T \le b \\ r_2, & T > b \end{cases} $

Effective rate (if $T>0$):

$ \text{ER} = \dfrac{\text{Tax}}{T} $

Glossary of Variables

Filing Status: Your Montana filing category (Single, Married Filing Jointly, Married Filing Separately, Head of Household).
Tax Year: The calendar tax year for which the tax is computed (currently 2024 or 2025).
Montana Taxable Income (T): Your income subject to Montana tax after state adjustments.
Lower Rate (r₁): The percentage applied to income up to the threshold.
Higher Rate (r₂): The percentage applied to the portion of income above the threshold.
Threshold (b): The income cutoff separating the lower and higher rates. It may differ by filing status and year.
Tax at Lower Rate (LB): $ \min(T,b)\times r_1 $
Tax at Higher Rate (UB): $ \max(T-b,0)\times r_2 $
Total Tax Before Credits: LB + UB, excluding refundable/nonrefundable credits.
Effective Rate (ER): Total tax divided by T, shown as a percentage.
Marginal Rate (MR): The rate that applies to your last dollar of income.

Worked Example: Step-by-Step

How It Works: A Step-by-Step Example

Assume Tax Year = 2025, Filing Status = Single, Taxable Income $T = \$60{,}000$. Defaults: lower rate $r_1=4.7\%$ and higher rate $r_2=5.9\%$. Threshold $b=\$41{,}000$.

Lower-bracket portion: $ \min(60{,}000, 41{,}000)\times 0.047 = 41{,}000\times 0.047 = \$1{,}927.00 $
Upper-bracket portion: $ \max(60{,}000-41{,}000, 0)\times 0.059 = 19{,}000\times 0.059 = \$1{,}121.00 $
Total tax before credits: $ 1{,}927.00 + 1{,}121.00 = \$3{,}048.00 $
Marginal rate: $ r_2 = 5.9\% $ (because $T>b$)
Effective rate: $ 3{,}048 / 60{,}000 = 5.08\% $

Frequently Asked Questions (FAQ)

Does the calculator include Montana credits?

No. This tool computes the statutory tax before credits. Apply nonrefundable or refundable credits after the result.

What if I don’t know my Montana taxable income?

Check your Montana return instructions or prior Form 2. For 2024+, Montana conforms more closely to federal taxable income with state adjustments. When in doubt, consult the MT DOR or a tax professional.

Are thresholds different by filing status?

Yes. The calculator loads status-specific thresholds for the selected tax year. Use Advanced to override if new values are published.

Is this calculator suitable for nonresidents?

Yes, for the Montana-source taxable income portion. Your taxable base must reflect Montana-source income allocation.

How often are parameters updated?

We monitor MT DOR releases annually. Thresholds are indexed; when new values appear, we update defaults and note the change log.

Can I switch to another state?

Yes. Browse the Taxation category to find other state calculators with the same accessible UX.

Will my data be stored?

No. All calculations run in your browser. We do not persist inputs.

Tool developed by Ugo Candido. Content verified by the CalcDomain Editorial Team.
Last reviewed for accuracy on: September 13, 2025.