Montana Income Tax Calculator 2026

Montana Income Tax: 5.9% Flat Rate

Montana uses a flat income tax rate of 5.9%, meaning all taxable income is taxed at the same rate regardless of how much you earn. Montana switched to a flat tax in 2024 from a previous seven-bracket graduated system.

On top of the 5.9% state tax, Montana residents also pay federal income tax ranging from 10% to 37%. This calculator combines both federal and Montana state tax to show your total liability, effective rate, and take-home pay.

How Montana's Flat Tax Compares

A flat tax simplifies filing — you pay 5.9% on all taxable income without navigating multiple brackets. Compared to the national median top state rate of around 5.5%, Montana's 5.9% rate is above average. For a single filer earning $100,000, the Montana state tax would be approximately $5,900.

States with flat taxes tend to have simpler returns and more predictable tax bills. The trade-off is that lower-income residents pay the same percentage as higher earners, unlike graduated systems where rates increase with income.

Reducing Your Montana Tax Bill

While you cannot change the flat rate, you can reduce your taxable income. Contributions to traditional 401(k) and IRA accounts reduce both your federal and Montana state taxable income. The 2026 401(k) limit is $24,500 ($32,500 with catch-up for age 50+). HSA contributions are also pre-tax for both federal and state purposes in most states.