What makes Colorado different

Colorado’s income tax looks like the simplest in the country: one flat rate, no local income taxes, a return that starts from the federal number and asks a short list of questions. Most of that is true. The complexity is somewhere else: in a refund written into the constitution, credits that switch on and off with the state’s revenue forecast, and a handful of income lines where one dollar changes everything. Here are the ten things to know.

1. One flat rate, and the voters own it

Every Colorado taxpayer pays 4.40% on taxable income, from the first dollar to the last. The constitution requires a single rate, and under TABOR the legislature cannot raise it without a vote of the people. Voters have cut it twice at the ballot box since 2020 (from 4.63% to 4.55%, then to 4.40%), and on November 3, 2026 they decide Amendment 87, which would replace the flat tax with six brackets from 3.7% to 8.4% starting in 2027. The outcome (verify) will be posted on the updates page.

Why it matters: there is no bracket planning in Colorado today. Shifting income between years saves nothing on the state side unless you are near one of the cliffs below. That could change in 2027.

2. TABOR: when the state collects too much, you get it back. Sometimes.

The Taxpayer’s Bill of Rights, a constitutional amendment the voters passed in 1992 (verify), caps state revenue at inflation plus population growth. Anything above the cap is refunded, and the legislature decides how: a temporary rate cut, a flat sales tax refund by income tier, or reimbursing counties for the senior property tax exemption first. The result is that your “refund” swings wildly.

Why it matters: you only get the refund if you file, even with no income. And several big credits (below) are switched on or off by the same surplus math. Don’t budget on last year’s Colorado refund.

3. Credits that come and go with the economy

Colorado has started tying tax credits to the state’s revenue forecast. The family affordability credit, worth up to $3,273 per young child in 2025, is gone for 2026 because the forecast missed its trigger. The earned income credit match dropped from 50% to 25% for the same reason. The EV, heat pump and e-bike credits were cut in half for 2026 by a growth trigger. None of this required a vote; it was written into the credits from the start.

4. Colorado follows federal law automatically, until the legislature says no

Your Colorado return starts from federal taxable income, and Colorado adopts federal tax law changes as they happen (“rolling conformity”). So when Congress created deductions for tips, overtime and seniors in July 2025, they cut Colorado tax too, instantly, without the legislature doing anything. The legislature then picks and chooses what to take back: overtime gets added back starting 2026; tips and the senior deduction do not; the QBI addback for high earners was made permanent.

Why it matters: every federal change ripples into Colorado, and the ripple can be undone a year later. Overtime earners should expect Colorado tax on overtime in 2026 even though the IRS doesn’t tax it.

5. One of the friendliest states for retirees

Colorado does not tax Social Security at all once you are 65, and since 2025 not between 55 and 64 either if your AGI is $75,000 or less single, $95,000 joint. Each person 65 or older also gets up to $24,000 for pension, IRA and 401(k) income ($20,000 from 55 to 64), but that cap is shared: the Social Security subtraction uses it up first, and only the rest is left for other retirement income. Add the federal standard deduction and the $6,000 senior deduction, and a retired couple drawing $50,000 of Social Security and $48,000 of IRA withdrawals can still owe Colorado nothing.

Why it matters: if you are weighing where to retire, Colorado is competitive with the no-income-tax states for ordinary retirement income. And if you are 55 to 64, the $75,000 / $95,000 line is a cliff worth planning around. The details are in Colorado for retirees.

6. The $300,000 cliff: where your deductions disappear

Once federal AGI hits $300,000, Colorado adds back most of your federal standard or itemized deduction. For 2025 the allowance was $12,000 single / $16,000 joint; for 2026, under Proposition MM, it falls to $1,000 / $2,000. At $500,000 single / $1,000,000 joint, business owners also add back the entire 20% qualified business income deduction. There is no phase-in; one dollar over the line triggers the whole thing. Colorado calls this the deduction addback, and it takes charitable gifts along with everything else: above the line, a gift to your church saves no Colorado tax at all.

Why it matters: a bonus, a stock sale or a Roth conversion that pushes you over $300,000 in a single year can cost roughly $1,000 to $2,000 of Colorado tax that careful timing would have avoided. See Give it away, pay tax anyway.

7. Big, refundable credits for working families and care workers

Colorado has quietly built one of the larger state family-credit systems in the country: a child tax credit of up to $1,200 per child under 6, a child care credit that is a share of the federal one, an EITC match, the family affordability credit in surplus years, and $1,200 credits for child care and long-term care workers. All of them are refundable and most are available to ITIN filers. A low-income family can get several thousand dollars from Colorado while owing no Colorado tax.

Why it matters: if you have young kids and modest income, filing a Colorado return is worth real money even when you owe nothing. National software and chain preparers miss these regularly.

8. Business owners: the SALT Parity election

The federal cap on deducting state and local taxes hits owners of profitable S corporations and partnerships. Colorado lets the business elect to pay the 4.40% at the entity level, where it is fully deductible federally, and the owners get a credit on their personal returns. The trade: the owners add back their QBI deduction for Colorado purposes. It has to be elected on the business return every year.

Why it matters: for an owner with $300,000 of pass-through income, the election can be worth a few thousand dollars of federal tax a year. It is a calculation, not a reflex; sometimes the QBI addback costs more than the federal savings.

9. People move here, and the move is where returns go wrong

Colorado taxes part-year residents and nonresidents only on Colorado-source income, apportioned on Form DR 0104PN. The hard questions are the ones a national preparer doesn’t ask: when did you actually become a resident, which state gets the stock options that vested across the move, where was the house sold, is the pension sourced to the state you live in now (it is), and does your old state give a credit for Colorado tax or the other way around.

Why it matters: move-year returns are the ones preparers amend most often for new clients. Get the residency date and the income sourcing right the first time.

10. What Colorado doesn’t do

No local income tax (a few cities charge a small occupational tax through payroll). No separate Colorado standard deduction or exemptions. No tax on Colorado municipal bond interest, but other states’ bonds are taxed. No estate or inheritance tax. No extension form; the six months is automatic. And no extension to pay: 90% has to be in by April 15.