Colorado's income tax system is one of the simplest in the United States: a flat 4.4% rate applies to all taxable income, regardless of how much you earn. There are no brackets, no phase-outs based on income, and no complex calculations β just a single rate applied after subtracting the standard deduction ($16,100 for single filers in 2026).
Colorado also has a unique constitutional provision called TABOR (Taxpayer's Bill of Rights) that requires excess state revenue to be refunded to taxpayers. In recent high-growth years, this has temporarily reduced the effective income tax rate below 4.4%. Social Security is fully exempt, property taxes average a very low ~0.51%, and no Colorado city imposes a local income tax β making Colorado one of the more tax-efficient states in the Mountain West.
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β Not for simple single-state returns. Free filing is fine for straightforward W-2 situations.
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