Data Source and Methodology
Authoritative data source: Colorado Department of Revenue — Individual Income Tax Guide. Latest publication and forms: “DR 0104 Individual Income Tax Book” (Tax Year 2024), updated 2024-12. Direct resource: https://tax.colorado.gov/individual-income-tax-guide
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
- Colorado applies a flat state income tax rate to Colorado taxable income.
- Colorado starts from federal taxable income, which already includes the federal standard deduction or itemized deductions.
- This calculator models that approach by letting you choose Standard vs. Itemized and by applying Colorado’s flat rate for the selected year.
The Formula Explained
AGI = \max\{0,\; \text{Gross Income} - \text{Pre-tax Deductions}\}
D = \begin{cases}
\text{StdDed}_{(year,status)} & \text{if Standard} \\
\text{Itemized Amount} & \text{if Itemized}
\end{cases}
TI = \max\{0,\; AGI - D\}
Tax_{pre} = TI \times r_{(year)}
Tax_{owed} = \max\{0,\; Tax_{pre} - \text{Credits}\}
\text{Effective Rate} = \begin{cases}
\frac{Tax_{owed}}{\text{Gross Income}} & \text{if Gross} > 0 \\
0 & \text{otherwise}
\end{cases}
Where r(year) is the Colorado flat rate (4.40% for 2024–2025). StdDed uses the federal standard deduction for the selected filing status and year.
Glossary of Variables
- Annual gross income: Total income before pre-tax deductions.
- Pre-tax deductions: Amounts excluded before federal tax (e.g., traditional 401(k), HSA).
- Standard deduction: Federal standard deduction based on filing status and year.
- Itemized deductions: Alternative to standard; enter your total if itemizing.
- Colorado taxable income (TI): AGI minus deductions (not below zero).
- Colorado flat tax rate (r): 4.40% for TY 2024–2025.
- Credits: Colorado credits that reduce tax due (not refundable in this simplified model).
- Effective state tax rate: Final tax owed divided by gross income.
How It Works: A Step-by-Step Example
Scenario: Tax Year 2024, Single filer, $85,000 gross income, $6,000 pre-tax deductions, using Standard deduction, $200 Colorado credits.
- AGI = max(0, 85,000 − 6,000) = 79,000
- Standard deduction (2024 Single) = 14,600
- Taxable income TI = max(0, 79,000 − 14,600) = 64,400
- Tax before credits = 64,400 × 0.044 = 2,833.60
- Credits applied = 200 → Tax owed = 2,833.60 − 200 = 2,633.60
- Effective rate = 2,633.60 / 85,000 ≈ 3.10%
Frequently Asked Questions (FAQ)
Is the Colorado state income tax flat?
Yes. Colorado levies a flat tax rate (4.40% in 2024–2025) on Colorado taxable income.
How does the calculator treat the standard deduction?
It mirrors the federal approach: you select Standard or Itemized. The standard deduction is based on your year and filing status.
Can I model itemizing vs. the standard deduction?
Yes. Toggle the deduction method and enter your itemized total to compare outcomes.
Do TABOR sales tax refunds affect this estimate?
Potential TABOR refunds are not part of the state income tax computation and are not included here.
Are payroll taxes or federal taxes included?
No. The calculator focuses on Colorado state income tax only.
What if my credits exceed the pre-credit tax?
The tool caps credits so tax owed doesn’t go below zero. Some credits may be refundable in reality; consult official guidance.
Where can I verify the rules?
See the Colorado Department of Revenue’s Individual Income Tax Guide: tax.colorado.gov/individual-income-tax-guide.