In our 510,000-path Monte Carlo study of 30-year retirement outcomes, Montana retirees finished at 73.53% success rate (ranked #30 of 51 by success rate, #35 of 51 by lowest median lifetime state tax). Median 30-year state-tax cost: $71,190 — that is $71,190 more than a Wyoming retiree pays. Median terminal balance after 30 years: $859,237. State tax is part of the optimization here — the playbook below shows the federal-state-ACA stack.
The MT verdict
For a retiree planning withdrawals in 2026, Montana is a middle-of-the-road state for retirement taxation. Still taxes social security in full, at every income level.
Montana has no dollar-capped retirement-income exclusion, so every converted dollar enters the state tax base. The marginal cost of a conversion here is the federal bracket plus the state rate plus, below 65, whatever premium tax credit crossing the 400% FPL cliff would cost you.
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. The Montana state tax on that conversion is approximately $1,695 — the full amount is taxed at 5.65%. 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 $84,600 — they lose their full ACA premium tax credit, roughly $12,000. Total cost of the $30,000 conversion: about $20,295, or an effective 67.7% marginal rate. That state figure uses Montana's top bracket rate, so read it as a ceiling: a household whose income lands in a lower bracket pays less, and Montana's own deductions reduce it further. The federal-state-ACA stack matters in Montana.
Cost breakdown
| Component | Amount |
|---|---|
| Federal income tax (22% bracket) | $6,600 |
| Montana state income tax | $1,695 |
| ACA premium tax credit clawback | $12,000 |
| Total cost on $30,000 conversion | $20,295 (67.7% effective) |
Scenario B (moderate): cliff-aware $40k conversion in Montana
A Montana couple aged 60, both on Marketplace coverage with $50K wages converts $40,000 but stops at exactly the 400% FPL cliff to preserve their PTC. State tax: $2,260 — the full amount is taxed at 5.65%. Federal tax at 22%: $8,800. ACA PTC preserved. Total cost: $11,060, or 27.7% effective. In moderate-tax states, the conversion size is bounded by both the IRMAA two-year lookback and the ACA cliff — not state tax alone.
What the Monte Carlo data says about Montana
QuantCalc Research ran a 30-year, 10,000-path Monte Carlo simulation for an identical representative retiree (age 60, $2M starting balance, 60/40 portfolio, $80K real annual spend) in each of the 51 U.S. jurisdictions. Here's how Montana compared to the best- and worst-case states:
| Metric | Montana | Wyoming (best) | California (worst) |
|---|---|---|---|
| 30-year success rate | 73.53% | 77.11% | 69.03% |
| Rank (of 51) | #30 | #1 | #51 |
| Median lifetime state tax (30y) | $71,190 | $0 | $154,980 |
| Median total tax (30y) | $289,590 | $218,400 | $373,380 |
| Median terminal balance | $859,237 | $999,751 | $695,612 |
| Δ success vs Wyoming | -3.58 pp | — | −8.08 pp |
Sources: QuantCalc 51-State Monte Carlo Study (2026-05-12) — 510,000 total paths, methodology fully documented and dataset released CC-BY-4.0. Montana's row in the dataset uses the same portfolio + spend + retirement age as every other state — the only variable is state tax treatment.
How Montana treats capital gains in retirement
Montana taxes long-term capital gains as ordinary income at the same top bracket rate (5.65%). That stacks on top of federal LTCG (0%/15%/20%) and the 3.8% NIIT for high earners. A 'free' federal 0% LTCG harvest still costs you up to 5.65% at the state level — meaningful in this jurisdiction, particularly during Roth-conversion years when your MAGI is already elevated.
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: $62,600
- Household of 2: $84,600
- Household of 3: $106,600
- Household of 4: $128,600
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 live cliff widget above for a quick check.
- Stay under the cliff if you can. In Montana at 5.65%, 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 the 0% LTCG bracket. Montana taxes long-term capital gains as ordinary income at the same top bracket rate (5.65%). That stacks on top of federal LTCG (0%/15%/20%) and the 3.8% NIIT for high earners. A 'free' federal 0% LTCG harvest still costs you up to 5.65% at the state level — meaningful in this jurisdiction, particularly during Roth-conversion years when your MAGI is already elevated.
- 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. See RMD + IRMAA calculator for the lookback math.
State tax basics for Montana retirees
| Question | Montana |
|---|---|
| State income tax | 5.65% top marginal |
| Number of brackets | 2 |
| Social Security taxed | Yes |
| 401(k) / Traditional IRA taxed | Yes |
| Retirement-income exclusion (couple) | None |
| Roth conversion draws that exclusion | Not applicable |
| State estate / inheritance tax | No |
| Retirement-friendliness tier | moderate |
| Notable feature | still taxes Social Security in full, at every income level |
| 30-yr MC success rate (rank) | 73.53% (#30/51) |
| Median 30-yr state tax | $71,190 |
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.
- State Retirement Tax Data 2026 — the per-jurisdiction rate, exclusion and Social Security figures behind this page, as CSV and JSON.
- 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.
- RMD + IRMAA Calculator — Medicare premium surcharge based on 2-year-old MAGI.
- Safe Withdrawal Rate Calculator — sequence-of-returns-aware withdrawal planning.
- Research: 51-State 30-year Monte Carlo (2026) — full ranking and dataset.
- 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. A $30,000 conversion by a couple aged 58 costs about $1,695 in state tax alone — the full amount is taxed at 5.65% — on top of federal tax and any ACA subsidy clawback. That state figure uses Montana's top bracket rate, so read it as a ceiling: a household whose income lands in a lower bracket pays less, and Montana's own deductions reduce it further.
What is Montana's 30-year Monte Carlo retirement success rate?
In QuantCalc's 510,000-path Monte Carlo study, a representative retiree in Montana (age 60, $2M balance, 60/40 portfolio, $80K real spend) finished 30 years at 73.53% success rate — ranked #30 of 51 jurisdictions. Median 30-year state tax: $71,190. Median terminal balance: $859,237.
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 — $84,600. 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 social security in full, at every income level. In our Monte Carlo ranking it placed #30 of 51 jurisdictions.
Does Montana tax Social Security benefits?
Yes — Montana taxes Social Security benefits. Social Security is taxed in full, at every income level — there is no AGI exemption threshold at all (this state conforms to the federal taxable-SS amount).
Does Montana tax 401(k) and IRA withdrawals?
Yes — Montana taxes 401(k) and traditional IRA withdrawals as ordinary income, at a top bracket rate of 5.65%.
Does Montana have a state estate or inheritance tax?
No — Montana does not impose a state-level estate or inheritance tax.
How does Montana tax capital gains?
Montana taxes long-term capital gains as ordinary income at the same top bracket rate (5.65%). That stacks on top of federal LTCG (0%/15%/20%) and the 3.8% NIIT for high earners. A 'free' federal 0% LTCG harvest still costs you up to 5.65% at the state level — meaningful in this jurisdiction, particularly during Roth-conversion years when your MAGI is already elevated.
Last updated 2026-08-23. State income tax figures reflect the 2026 schedule published by Montana's tax authority. ACA poverty-level figures from HHS 2026 Federal Register. Monte Carlo numbers from the QuantCalc 51-state research drop (2026-05-12, CC-BY-4.0). This page is educational. Not tax, legal, or financial advice — consult a qualified advisor.