Montana Payroll Tax Calculator: Rates, Withholding, and Deadlines

Montana payroll tax withholding means running three separate calculations against each paycheck: federal income tax under IRS tables, FICA at 7.65% (6.2% Social Security up to the 2026 wage base of $184,500, plus 1.45% Medicare on all wages), and Montana state income tax at 4.7% on the first $47,500 of taxable income for single filers or $95,000 for joint filers, and 5.65% above that.¹² On top of what you withhold from the employee, you pay the employer share of FICA, Montana unemployment insurance, and federal unemployment tax. Montana has no city or county income taxes, so state withholding is the only sub-federal income tax in the mix.

Forms and Information You Need Before the First Paycheck

Every employee fills out two withholding forms: the federal W-4 and Montana’s Form MW-4. Montana no longer accepts the federal W-4 for state withholding, so both documents have to be in the file before you cut a check.³ The MW-4 gives you the filing status and allowances that feed the Montana withholding formula.

You also need each worker’s gross wages for the pay period and any pre-tax deductions such as health premiums, 401(k) contributions, or FSA elections. Pre-tax deductions reduce the taxable wage base for income tax, though not for FICA in the case of 401(k) contributions.

First, confirm the person is actually an employee. Montana defines an independent contractor as someone free from control over how the work is performed and engaged in an independently established trade or business. Handing someone a 1099 or signing a labor agreement does not make them a contractor, and misclassification carries fines up to $5,000 per violation.⁴ If you control how the work gets done, that worker is an employee for payroll tax purposes.

Federal Income Tax

Federal income tax runs on a seven-bracket progressive schedule for 2026: 10%, 12%, 22%, 24%, 32%, 35%, and 37%. A single filer, for example, pays 10% on the first $12,400, 12% up to $50,400, 22% up to $105,700, and so on through the top bracket at $640,600. Married-filing-jointly thresholds are roughly double.⁵

What you actually withhold each period depends on the employee’s W-4, pay frequency, and gross wages net of pre-tax deductions. IRS Publication 15-T contains the percentage-method and wage-bracket tables that turn those inputs into a dollar figure. Payroll software handles this; if you’re calculating manually, Publication 15-T is the reference.

Social Security and Medicare

Social Security tax is 6.2% of gross wages up to the 2026 wage base of $184,500. Once year-to-date wages cross that line, Social Security withholding stops for the rest of the year. Medicare is 1.45% on every dollar of wages with no cap. Both are matched by the employer, so the combined employer FICA cost is 7.65%.²

Once an employee’s wages pass $200,000 in a calendar year, you also begin withholding an Additional Medicare Tax of 0.9% on every dollar above that threshold. This one has no employer match. The $200,000 mark applies for withholding regardless of the employee’s filing status; couples reconcile at a higher $250,000 threshold when they file.⁶

Montana State Income Tax

For 2026, Montana taxes the first $47,500 of taxable income at 4.7% and everything above at 5.65% for single filers and married-filing-separately. Joint filers get the same rates with the bracket line doubled to $95,000.¹

For paycheck-level withholding, the Department of Revenue publishes a formula and tables. The 2026 formula is W = A + (B × (G − C)), where G is gross earnings for the pay period and A, B, and C come from the table matched to the employee’s pay frequency and filing status.⁷ For a single employee paid biweekly, the first $619 of period earnings falls in a zero-withholding zone (reflecting the built-in standard deduction), earnings from $619 to $2,446 are withheld at 4.7%, and anything above $2,446 is withheld at 5.65%. Round up to the nearest dollar.

Bonuses and Supplemental Wages

When you pay a bonus, commission, or other supplemental wage separately from regular pay, Montana gives you three ways to compute state withholding: combine it with the current period’s regular wages and withhold on the total, combine it with the most recent regular payroll in the same calendar year and withhold on that total, or apply a flat 5% to the supplemental amount.⁷ The flat 5% is the easiest for one-off payments.

Employer-Only Taxes: Unemployment Insurance

Unemployment insurance is paid entirely by the employer. Nothing comes out of the employee’s check for it.

Montana’s SUI taxable wage base is $47,300 in 2026, set annually at 80% of the state average annual wage rounded to the nearest $100. Your rate depends on your experience rating. Schedule 1 is in effect for 2026: positive-reserve employers pay 0.00% to 1.22%, and deficit employers pay 2.72% to 6.12%. Every employer also pays a 0.18% Administrative Fund Tax on top. New employers without three years of history receive industry-based rates, from 1.00% for most industries up to 2.00% for construction and unclassified establishments.⁸

FUTA applies to the first $7,000 of each employee’s wages at a nominal 6.0%.⁹ Employers who pay state unemployment in full and on time get a 5.4% credit, cutting the effective rate to 0.6%. Montana is not a credit reduction state, so most Montana employers pay the 0.6% rate — a maximum of $42 per employee per year.¹⁰

A Worked Paycheck

Take a single employee paid biweekly at $3,000 gross with a $150 401(k) contribution.

Gross wages: $3,000.
Taxable wages for income tax after the 401(k): $2,850.
Federal income tax: from IRS Publication 15-T using the employee’s W-4 and $2,850.
Social Security: 6.2% of $3,000 = $186. (FICA runs off gross; the 401(k) does not reduce it.)
Medicare: 1.45% of $3,000 = $43.50.
Montana state tax, biweekly single: $0 on the first $619, 4.7% on $619 to $2,446 ($85.87), 5.65% on $2,446 to $2,850 ($22.83), rounded up to $109.
Net pay: $3,000 minus the 401(k), federal tax, $186, $43.50, and $109.

Employer costs on the same paycheck sit on top: matching $186 in Social Security, matching $43.50 in Medicare, SUI at your experience rate on wages up to the $47,300 annual cap, the 0.18% Administrative Fund Tax, and 0.6% FUTA on the first $7,000 of annual wages. Those add roughly 8% to 14% to the true cost of each wage dollar, depending on your SUI rate.

Deposit and Filing Deadlines

State Withholding Deposits

How often you remit Montana withholding depends on how much you withheld during the lookback period, July 1 of the prior year through June 30 of the current year.¹¹

Annual filer, up to $1,199 withheld: one payment due January 31.
Monthly, $1,200 to $11,999: due the 15th of the following month.
Accelerated, $12,000 or more: same schedule as federal deposits, based on payday.

New withholding accounts start monthly. The department reviews the lookback each year and notifies you by November 1 if your schedule will change.

Quarterly Unemployment Reports

SUI wage reports and payments follow a fixed calendar:¹²

Q1 (Jan–Mar): April 30.
Q2 (Apr–Jun): July 31.
Q3 (Jul–Sep): October 31.
Q4 (Oct–Dec): January 31.

If a deadline falls on a weekend or holiday, it shifts to the next business day. File the quarterly report even if you paid no wages that quarter.

Penalties If You Miss

Montana penalties come from two directions, and interest accrues from day one.

Late filing: the greater of $50 or 5% of unpaid tax per month or partial month, capped at 25%.
Late payment of withholding: 1.5% per month of the unpaid balance, capped at 15%.
Interest for 2026: 10.25% annually on withholding, computed daily at 0.028082% starting on the original due date.

A return that is both filed and paid late gets both penalties at once.¹³

Two relief paths exist. If you pay the full tax plus interest within 30 days of a department notice, the late payment penalty is waived automatically. For circumstances beyond your control, you can request a reasonable-cause waiver on Form APLS101F or by written letter. Reasonable cause means you used ordinary business care and still could not meet the deadline; being busy or forgetting does not qualify.¹³

One Related Cost: Workers’ Compensation

Workers’ comp isn’t a payroll tax, but it’s a payroll-linked cost Montana law requires. Any employer with at least one employee must carry coverage under an approved plan, with premiums quoted per $100 of covered payroll and rates set by industry risk classification.¹⁴ Sole proprietors, working partners, member-managed LLC members, and corporate officers owning at least 10% of stock can opt out, and the officer exemption extends to close family members. Once you hire anyone outside that circle, coverage is required.

1
Montana Legislature. Montana Code 15-30-2103 – Rate of Tax
2
Social Security Administration. Contribution and Benefit Base
3
Montana Department of Revenue. Montana Tax Allowances and Exemptions (Form MW-4)
4
Montana Department of Labor & Industry. Independent Contractor Exemption Certificates
5
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
6
Internal Revenue Service. Topic No. 560, Additional Medicare Tax
7
Montana Department of Revenue. Montana Employer and Information Agent Guide with Tax Tables
8
Montana Department of Labor & Industry. Unemployment Insurance Contribution Taxable Wage Base and Rates
9
Internal Revenue Service. Topic No. 759, Form 940 – FUTA Tax Return
10
U.S. Department of Labor. FUTA Credit Reductions
11
Montana Department of Revenue. Montana Wage Withholding Returns and Payments
12
Legal Information Institute. Montana Admin. r. 24.40.1609 – Due Date of Taxes and Quarterly Reports by Employers
13
Montana Department of Revenue. Interest and Penalties
14
Montana Legislature. Montana Code 39-71-401 – Employments Covered and Exemptions