Proposition 136 Would Cap Colorado’s Income Tax Rate at 4.4% 

Colorado voters will decide this November whether to place a 4.4% statutory cap on the state’s individual and corporate income tax rates. 

Proposition 136 would establish Colorado’s current 4.4% income tax rate as the maximum rate beginning in 2027, applying to both individual and corporate income taxes.

Colorado already has one of the nation’s best-known taxpayer safeguards in the Taxpayer’s Bill of Rights (TABOR), which requires voter approval for tax increases. Proposition 136 would add another statutory protection by explicitly setting 4.4% as the maximum individual and corporate income tax rate. 

The measure comes as Colorado voters are simultaneously considering a competing proposal that would fundamentally change the state’s income tax system. 

Amendment 87 would eliminate Colorado’s 4.4% flat individual and corporate income tax and replace it with six brackets ranging from 3.7% to 8.4%. The state’s official analysis estimates the proposal would generate nearly $2 billion in additional annual revenue once fully implemented. 

Proposition 136 would instead preserve 4.4% as the statutory ceiling on Colorado’s income tax rates. 

Colorado voters have reduced the state’s income tax rate twice in the last six years. In 2020, voters approved Proposition 116, reducing the individual and corporate income tax rate from 4.63% to 4.55%. Two years later, voters approved Proposition 121, lowering the rate again from 4.55% to its current 4.4%. 

Proposition 121 passed with approximately 65% of the vote. The official 2026 Blue Book cites that result in presenting the argument for Proposition 136, stating that the measure would reinforce voter support for maintaining the existing rate. 

Colorado’s flat tax also has a longer history. The state moved from a graduated income tax to a single-rate system beginning in 1987 and has maintained it ever since. 

Supporters of Proposition 136 argue that the measure would reinforce the 4.4% rate voters approved in 2022 and provide an additional statutory barrier against higher individual and corporate income tax rates.

The two measures give Colorado voters separate decisions over the future structure of the state’s income tax. Amendment 87 would replace the existing flat tax with rates reaching 8.4%. Proposition 136 would establish the existing 4.4% rate as the statutory maximum.