Colorado's flat tax (1986-2026)
Colorado replaced its graduated income tax with a single rate in the 1980s, and a constitutional provision required every taxpayer to pay the same percentage. The rate sat at 4.4% before Amendment 87.
The flat rate became part of the state's pitch to affluent newcomers and businesses.
It held for four decades, until 51.4% of voters approved six brackets and removed the uniform-rate requirement.
Amendment 87 is the first structural rewrite of Colorado's income tax since the flat rate took hold.
