SSDI Taxes in Montana: What You Need to Know About Federal and State Rules

If you receive Social Security Disability Insurance in Montana — or you're applying and wondering what a future benefit might cost you at tax time — there are two separate systems to understand: federal income tax on SSDI and Montana's own state income tax rules. They don't work the same way, and the gap between them matters.

How Federal Taxes on SSDI Work

SSDI is not automatically tax-free. The IRS uses a formula called combined income to determine whether your benefits are taxable at the federal level.

Combined income = Adjusted Gross Income + Nontaxable Interest + 50% of your SSDI benefits

Once you calculate that number, here's how the federal thresholds work:

These thresholds have not been adjusted for inflation since they were established, which means more recipients cross them over time simply due to cost-of-living increases in their other income sources.

One important point: "up to 85%" is the maximum portion of SSDI that becomes taxable income. It does not mean you pay 85% in tax. It means up to 85 cents of every SSDI dollar gets added to your taxable income, where your regular marginal rate then applies.

🏔️ Montana's State Income Tax on SSDI

Montana is one of the states that does tax Social Security benefits at the state level — but the rules have changed significantly in recent years.

Under Montana law that took effect for tax year 2024, the state moved to a simplified approach. Montana no longer follows the federal combined income formula for Social Security taxation. Instead:

• Montana taxpayers with federal adjusted gross income (AGI) of $25,000 or less (single filers) or $32,000 or less (married filing jointly) are exempt from state tax on Social Security benefits.
• Above those thresholds, a portion of Social Security income — including SSDI — may be included in Montana taxable income.

Montana's income tax rates for 2024 onward are structured under a two-bracket system: 4.7% on income up to $20,500 and 5.9% on income above that (amounts adjust annually, so confirm current brackets with the Montana Department of Revenue). This is a notable simplification from the previous multi-bracket system.

The result: for lower-income SSDI recipients in Montana with little or no other income, state taxes on their benefits may be minimal or zero. For those with additional income — a working spouse, investment earnings, a pension, or partial wages — the calculation changes.

Variables That Shape Your Tax Exposure

No two SSDI recipients face the same tax picture. The factors that determine your actual tax burden include:

Income sources beyond SSDI. SSDI alone, for many recipients, falls below both federal and state thresholds. What tips people into taxable territory is usually other income — a spouse's wages, withdrawals from retirement accounts, rental income, or freelance work kept under SSA's Substantial Gainful Activity (SGA) limits.

Filing status. Married couples have higher combined income thresholds, but they also pool income, which can push combined figures higher. Single filers have lower thresholds but usually only one income stream.

Back pay lump sums. SSDI applicants who wait months or years for approval often receive a lump sum back payment covering the period since their established onset date. The IRS allows you to allocate that lump sum across prior tax years using a method called lump-sum election, which can reduce the portion taxed in a single year. Montana generally conforms to federal treatment in this area, but the interaction with state rules is worth tracking carefully.

Workers' compensation offset. If your SSDI benefit has been reduced due to a workers' compensation offset, only the SSDI amount you actually receive counts toward combined income calculations — not the notional pre-offset figure.

SSI vs. SSDI. This distinction matters. Supplemental Security Income (SSI) is not taxable at the federal level, and Montana does not tax SSI either. SSDI, funded through payroll taxes and tied to your work record, is the program subject to the tax rules described above. If you receive both, only the SSDI portion is subject to potential taxation.

💡 When SSDI Recipients Are Most Likely to Owe Tax

• Married households where one spouse works
• Recipients who also receive a pension or annuity
• Those who took a lump-sum back payment in the same year they had other income
• Recipients who returned to part-time work within SSA's Trial Work Period or Extended Period of Eligibility and reported wages

When SSDI Recipients Are Less Likely to Owe Tax

• Single filers with no income outside their SSDI benefit
• Recipients whose only other income is SSI (which isn't counted)
• Those whose combined income falls below federal and Montana thresholds

The Missing Piece

The federal rules and Montana's updated framework create a landscape where taxation of SSDI is real but far from universal — and whether it applies to you, and how much, depends entirely on the composition of your household income, your filing status, whether you received back pay, and what other benefits or earnings entered the picture that year. The rules are knowable. Applying them accurately to your own return is where individual circumstances take over.