In our 510,000-path Monte Carlo study of 30-year retirement outcomes, Colorado retirees finished at 73.98% 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. One flat bracket, with a social security and pension subtraction that turns fully exempt at 65.
Colorado 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 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. The Colorado state tax on that conversion is approximately $1,320 — the full amount is taxed at 4.40%. 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 $19,920, or an effective 66.4% marginal rate. Colorado applies one rate to all taxable income, so that state figure is the full amount before any deduction Colorado allows. 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: $1,760 — the full amount is taxed at 4.40%. Federal tax at 22%: $8,800. ACA PTC preserved. Total cost: $10,560, or 26.4% 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 | 73.98% | 77.11% | 69.03% |
| Rank (of 51) | #24 | #1 | #51 |
| Median lifetime state tax (30y) | $55,440 | $0 | $154,980 |
| Median total tax (30y) | $273,840 | $218,400 | $373,380 |
| Median terminal balance | $891,583 | $999,751 | $695,612 |
| Δ success vs Wyoming | -3.13 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. 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 bracket 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 up to 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: $62,600
- Household of 2: $84,600
- Household of 3: $106,600
- Household of 4: $128,600
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 bracket 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 up to 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 |
| Retirement-income exclusion (couple) | None |
| Roth conversion draws that exclusion | Not applicable |
| State estate / inheritance tax | No |
| Retirement-friendliness tier | moderate |
| Notable feature | one flat bracket, with a Social Security and pension subtraction that turns fully exempt at 65 |
| 30-yr MC success rate (rank) | 73.98% (#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.
- 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 Colorado tax Roth conversions?
Colorado taxes Roth conversions as ordinary income at the state level. A $30,000 conversion by a couple aged 58 costs about $1,320 in state tax alone — the full amount is taxed at 4.40% — on top of federal tax and any ACA subsidy clawback. Colorado applies one rate to all taxable income, so that state figure is the full amount before any deduction Colorado allows.
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 73.98% 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 — $84,600. 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. One flat bracket, with a social security and pension subtraction that turns fully exempt at 65. In our Monte Carlo ranking it placed #24 of 51 jurisdictions.
Does Colorado tax Social Security benefits?
Yes — Colorado taxes Social Security benefits. Filers 65+ are fully exempt regardless of AGI. Filers 55-64 are exempt when AGI is at/below the threshold, else get a $20,000-capped subtraction. Filers under 55 get NO subtraction at all — Social Security is taxed in full, just like any other state that fully taxes SS. The AGI threshold is $75,000 for a single filer and $95,000 for a married couple filing jointly.
Does Colorado tax 401(k) and IRA withdrawals?
Yes — Colorado taxes 401(k) and traditional IRA withdrawals as ordinary income, at a top bracket rate of 4.40%.
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 bracket 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 up to 4.40% 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 Colorado'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.