The MT verdict
For a retiree planning withdrawals in 2026, Montana is a middle-of-the-road state for retirement taxation. Still taxes ss, $5,500 retirement exclusion.
There is meaningful state tax on Roth conversions, but the rate is not punitive. Modeling the joint federal + state + ACA cliff cost matters — small conversions can be efficient, large conversions less so.
Worked example: $30k Roth conversion in Montana
Consider a married couple age 58 in Montana with $75,000 of taxable income, both on ACA Marketplace coverage. They want to convert $30,000 from a traditional IRA to a Roth. At Montana's 5.90% top marginal rate, the state tax on that conversion is approximately $1,770. Federal tax at the 22% bracket adds another $6,600. And because the conversion pushes their MAGI to $105,000 — over the 400% FPL cliff of $81,760 — they lose their full ACA premium tax credit, roughly $12,000. Total cost of the $30,000 conversion: about $20,370, or an effective 67.9% marginal rate. The federal-state-ACA stack matters in Montana.
Cost breakdown
| Component | Amount |
|---|---|
| Federal income tax (22% bracket) | $6,600 |
| Montana state income tax | $1,770 |
| ACA premium tax credit clawback | $12,000 |
| Total cost on $30,000 conversion | $20,370 (67.9% effective) |
Why the ACA cliff hits hard in Montana
The 400% federal-poverty-level cliff is federal, not state-specific — but its dollar impact depends on the benchmark Silver-plan premium in your county. Montana's Marketplace pricing and your household composition determine the size of the subsidy at risk. A two-person household near 400% FPL can easily have $10,000–$15,000 of annual premium tax credit on the line. Under the OBBBA 2026 restoration of the cliff, $1 of additional MAGI above 400% FPL eliminates the entire credit.
For 2026 the 400% FPL threshold is:
- Household of 1: $60,240
- Household of 2: $81,760
- Household of 3: $103,280
- Household of 4: $124,800
Optimal Roth conversion strategy for Montana
The MT-specific playbook depends on tier:
- Identify your cliff distance. Compute MAGI from all income sources (wages, capital gains, interest, dividends, traditional withdrawals). Find your headroom under 400% FPL. Use the ACA cliff embed for a quick check.
- Stay under the cliff if you can. In Montana at 5.90%, the marginal cost of going over the cliff is federal tax + state tax + full PTC clawback. The break-even conversion size is smaller than in tax-free states.
- If you must go over, convert big. Once you've crossed the cliff, additional conversion dollars only cost federal + state tax (no incremental PTC loss). A "rip the bandage" conversion year can be efficient if you have many traditional dollars to move.
- Coordinate with capital gains and 0% LTCG bracket. In Montana, long-term capital gains stack with ordinary income. Time conversions in years when you have low-income headroom.
- Plan ahead for IRMAA. The IRMAA Medicare premium surcharge has a 2-year lookback. A Montana resident in their early 60s converting today will see IRMAA implications at 65.
State tax basics for Montana retirees
| Question | Montana |
|---|---|
| State income tax | 5.90% top marginal |
| Number of brackets | 2 |
| Social Security taxed | Yes (with thresholds) |
| 401(k) / Traditional IRA taxed | Yes |
| State estate / inheritance tax | No |
| Retirement-friendliness tier | moderate |
| Notable feature | still taxes SS, $5,500 retirement exclusion |
Model your full Montana retirement scenario
Free 10,000-path Monte Carlo with state-specific tax engine, ACA cliff, Roth conversion optimizer, IRMAA lookback — all in your browser, no signup.
Run a free simulation →Related calculators and reading
- All-states retirement tax comparison — see Montana alongside the other 50 jurisdictions.
- ACA Subsidy Cliff Optimizer — find the largest Roth conversion that keeps you under 400% FPL.
- Roth Conversion Optimizer — bracket-fill vs. fixed-amount strategy comparison.
- IRMAA Lookback Calculator — Medicare premium surcharge based on 2-year-old MAGI.
- Safe Withdrawal Rate Calculator — sequence-of-returns-aware withdrawal planning.
- Research: Monte Carlo ACA Cliff 2026 — 80,000-path study of the cliff cost.
FAQ
Does Montana tax Roth conversions?
Montana taxes Roth conversions as ordinary income at the state level. At a top marginal rate of 5.90%, a large conversion can add meaningful state-tax cost on top of federal tax and the ACA cliff.
What is the ACA cliff in Montana for 2026?
The ACA premium-tax-credit cliff is a federal threshold, not state-specific. For a household of two in 2026, it sits at 400% of the federal poverty level — $81,760. Crossing it by even $1 of MAGI eliminates the full subsidy under the OBBBA 2026 rules.
Is Montana a good state to retire for tax purposes?
Montana is a middle-of-the-road state for retirement taxation. Still taxes ss, $5,500 retirement exclusion.
Does Montana tax Social Security benefits?
Montana taxes Social Security benefits as part of state income. Some exemptions or income thresholds may apply.
Does Montana have a state estate or inheritance tax?
No — Montana does not impose a state-level estate or inheritance tax.
Last updated 2026-05-12. State income tax data sourced from the Montana Department of Revenue and the Tax Foundation's 2026 state tax facts publication. ACA poverty-level figures from HHS 2026 Federal Register. This page is educational. Not tax, legal, or financial advice — consult a qualified advisor.