Montana Bonus Tax Calculator 2026
Montana allows a flat 5% state withholding on a bonus paid separately — its guide uses a holiday bonus as the example.
Bonus check calculator
Three options in the employer guide
The Montana Employer and Information Agent Guide with Montana Withholding Tax Tables – 2026 says supplemental wages such as commissions, bonuses or overtime "are subject to withholding based on the total of the regular and supplemental wages." When they are paid separately — the guide's example is a holiday bonus — the employer can choose among three ways: add the bonus to the current payroll period's wages, add it to the last preceding payroll period in the same calendar year, or withhold "a flat 5 percent of the supplemental wage." This calculator uses the 5% option: $250.00 on $5,000, $125.00 on a $2,500 holiday bonus.
North Dakota reciprocity
Montana's Department of Revenue maintains a wage reciprocity agreement with North Dakota. If it covers your situation, you may be withheld for your home state instead — North Dakota's own supplemental option is 1.50% — so choose that state above.
Form MW-4
Montana uses its own withholding certificate, Form MW-4, for regular wages. The flat 5% option for a separate bonus does not depend on what the MW-4 says.
| Rule | Optional flat 5% on a separately paid bonus |
|---|---|
| Valid through | December 31, 2026 |
| Documents | Montana Employer and Information Agent Guide with Montana Withholding Tax Tables – 2026 (2026) |
| Agency | Montana Department of Revenue |
| Federal income tax | −$1,100.00 |
| Social Security | −$310.00 |
| Medicare | −$72.50 |
| Montana income tax | −$250.00 |
| Net | $3,267.50 |