Montana’s corporate return is due a month later than the federal date, its individual tax was simplified to two rates for 2024, and — a defining feature — the state has no general sales tax. It also offers an elective pass-through entity tax.
Montana Tax Deadlines at a Glance (2026)
Entity Type | Return Due | Extended Due Date |
|---|---|---|
Individuals (Form 2) | April 15, 2026 | October 15, 2026 |
C Corporations (Form CIT) | May 15, 2026 | November 15, 2026 |
S Corporations (Form PTE) | March 16, 2026 | September 15, 2026 |
Partnerships (Form PTE) | March 16, 2026 | September 15, 2026 |
The correction to note: Montana’s C-corporation return (Form CIT) is due May 15, 2026 — the 15th day of the 5th month — not April 15, with an automatic six-month extension to November 15. Individuals file by April 15 (extension to October 15), and S corporations and partnerships (Form PTE) follow the March 16, 2026 deadline (March 15 is a Sunday), extending to September 15.
A Two-Rate Individual Tax and No Sales Tax
Effective 2024, Montana collapsed its brackets to two rates: 4.7% and a 5.9% top rate (the top rate applying above roughly $21,100 single / $42,200 married). The corporate income tax is a flat 6.75%, with a $50 minimum. And Montana is one of the few states with no general sales tax — a meaningful simplification for businesses operating there.
The Elective PTE Tax
Montana’s elective pass-through entity tax (SB 554, effective 2023) lets partnerships and S corporations pay at the entity level at 5.9% of the owner’s distributive share of Montana-source income, giving owners a credit — a federal SALT-cap workaround. The election is made annually on a timely-filed Form PTE and is irrevocable for the year.
Estimates, Extensions, and Penalties
Individual estimated payments are due April 15, June 15, September 15, 2026, and January 15, 2027, required if you expect to owe more than $500. Montana applies uniform penalties and interest set annually; an extension covers filing only, with tax due at the original date.
CPA Action Steps
Use May 15 for the C-corp Form CIT — not April 15
File Form PTE (S-corps and partnerships) by March 16
Apply the two-rate 4.7%/5.9% individual and 6.75% corporate structure
Consider the 5.9% PTE election for SALT-cap relief
Verify current rates and dates against the Montana Department of Revenue (mtrevenue.gov) before filing.