In our 510,000-path Monte Carlo study of 30-year retirement outcomes, Colorado retirees finished at 73.97% success rate (ranked #24 of 51 by success rate, #23 of 51 by lowest median lifetime state tax). Median 30-year state-tax cost: $55,440 — that is $55,440 more than a Wyoming retiree pays. Median terminal balance after 30 years: $891,583. State tax is part of the optimization here — the playbook below shows the federal-state-ACA stack.
The CO verdict
For a retiree planning withdrawals in 2026, Colorado is a middle-of-the-road state for retirement taxation. Flat rate, ss deduction up to $24k age 65+.
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 Colorado
Consider a married couple age 58 in Colorado 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 Colorado's 4.40% top marginal rate, the state tax on that conversion is approximately $1,320. 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 $19,920, or an effective 66.4% marginal rate. The federal-state-ACA stack matters in Colorado.
Cost breakdown
| Component | Amount |
|---|---|
| Federal income tax (22% bracket) | $6,600 |
| Colorado state income tax | $1,320 |
| ACA premium tax credit clawback | $12,000 |
| Total cost on $30,000 conversion | $19,920 (66.4% effective) |
Scenario B (moderate): cliff-aware $40k conversion in Colorado
A Colorado 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 at 4.40% effective ~3.74%: $1,496. Federal tax at 22%: $8,800. ACA PTC preserved. Total cost: $10,296, or 25.7% 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 Colorado
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 Colorado compared to the best- and worst-case states:
| Metric | Colorado | Wyoming (best) | California (worst) |
|---|---|---|---|
| 30-year success rate | 73.97% | 77.07% | 67.91% |
| Rank (of 51) | #24 | #1 | #51 |
| Median lifetime state tax (30y) | $55,440 | $0 | $167,580 |
| Median total tax (30y) | $273,840 | $218,400 | $385,980 |
| Median terminal balance | $891,583 | $996,189 | $652,555 |
| Δ success vs Wyoming | -3.10 pp | — | −9.16 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. Colorado's row in the dataset uses the same portfolio + spend + retirement age as every other state — the only variable is state tax treatment.
How Colorado treats capital gains in retirement
Colorado taxes long-term capital gains as ordinary income at the same top marginal rate (4.40%). 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 4.40% 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 Colorado
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. Colorado'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 Colorado
The CO-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 Colorado at 4.40%, 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. Colorado taxes long-term capital gains as ordinary income at the same top marginal rate (4.40%). 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 4.40% 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 Colorado 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 Colorado retirees
| Question | Colorado |
|---|---|
| State income tax | 4.40% top marginal |
| Number of brackets | 1 |
| Social Security taxed | Yes (with thresholds) |
| 401(k) / Traditional IRA taxed | Yes |
| State estate / inheritance tax | No |
| Retirement-friendliness tier | moderate |
| Notable feature | flat rate, SS deduction up to $24K age 65+ |
| 30-yr MC success rate (rank) | 73.97% (#24/51) |
| Median 30-yr state tax | $55,440 |
Model your full Colorado 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 Colorado 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.
- 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 Colorado tax Roth conversions?
Colorado taxes Roth conversions as ordinary income at the state level. At a top marginal rate of 4.40%, a $30,000 conversion costs about $1,320 in state tax alone — on top of federal tax and any ACA subsidy clawback.
What is Colorado's 30-year Monte Carlo retirement success rate?
In QuantCalc's 510,000-path Monte Carlo study, a representative retiree in Colorado (age 60, $2M balance, 60/40 portfolio, $80K real spend) finished 30 years at 73.97% success rate — ranked #24 of 51 jurisdictions. Median 30-year state tax: $55,440. Median terminal balance: $891,583.
What is the ACA cliff in Colorado 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 Colorado a good state to retire for tax purposes?
Colorado is a middle-of-the-road state for retirement taxation. Flat rate, ss deduction up to $24k age 65+. In our Monte Carlo ranking it placed #24 of 51 jurisdictions.
Does Colorado tax Social Security benefits?
Colorado taxes Social Security benefits as part of state income. Some exemptions or income thresholds may apply.
Does Colorado have a state estate or inheritance tax?
No — Colorado does not impose a state-level estate or inheritance tax.
How does Colorado tax capital gains?
Colorado taxes long-term capital gains as ordinary income at the same top marginal rate (4.40%). 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 4.40% at the state level — meaningful in this jurisdiction, particularly during Roth-conversion years when your MAGI is already elevated.
Last updated 2026-05-16. State income tax data sourced from the Colorado Department of Revenue and the Tax Foundation's 2026 state tax facts publication. 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.