What Is Colorado Form 104? Filing, Credits, and Deadlines

Colorado Form 104 is the state individual income tax return filed each year with the Colorado Department of Revenue by full-year residents, part-year residents, and non-residents who earned income from Colorado sources. It applies Colorado’s flat 4.40% tax rate to your modified taxable income and reconciles what you owe against what was already withheld or paid.¹ The form starts with figures from your federal return and then adjusts them using Colorado-specific additions, subtractions, and credits, which is why you need to finish your federal Form 1040 before you can finish Form 104.²

Who Has to File It

If you’re a full-year Colorado resident and the IRS requires you to file a federal return, you also have to file Form 104.³ For the 2026 tax year the federal threshold is $16,100 of gross income for a single filer and $32,200 for a married couple filing jointly.

File anyway if your income is lower but Colorado tax was withheld from your pay. That return is the only way to get the withholding back. The same goes for the TABOR refund, the Earned Income Tax Credit, and the Property Tax/Rent/Heat rebate — skip the return and you forfeit the money.

Part-Year Residents and Non-Residents

Move into or out of Colorado during the year and you’re a part-year resident, taxed on everything you earned while living in the state plus any Colorado-sourced income afterward. Non-residents who never lived here but earned Colorado wages, rent, or business income have a filing obligation too.⁴ Both groups attach Form 104PN, which apportions total income so Colorado taxes only the share connected to the state.⁵ The filing trigger is Colorado-sourced gross income at or above the federal minimum.

Military and Military Spouses

Active-duty servicemembers stationed in Colorado but domiciled elsewhere don’t owe Colorado tax on their military pay, because orders alone don’t change legal residence under the Servicemembers Civil Relief Act. The Military Spouses Residency Relief Act extends similar protection to qualifying spouses, and Colorado’s Form DR 1059 lets a qualifying spouse claim exemption from Colorado withholding on wages earned in the state.⁶

How the Tax Is Calculated

Colorado doesn’t rebuild your income from scratch. Your federal taxable income is the starting line. From there you apply Colorado additions and subtractions, choose a deduction, and multiply what’s left by 4.40%.⁷ Always confirm the rate for the year you’re filing, since it has moved recently.¹

Additions

The most common addition is the state income tax addback. If you itemized federally and deducted state income tax, Colorado makes you add that deduction back, including premiums withheld for the state’s Paid Family and Medical Leave program. Property taxes, general sales taxes, and local income taxes you deducted federally don’t get added back. The addback is capped at the amount by which your itemized deductions exceeded the federal standard deduction you could have taken instead.⁸ Interest from other states’ municipal bonds is also added back, because Colorado taxes it even though the federal government doesn’t.

Subtractions

Subtractions are where Colorado gives real money back:

Retirement income: taxpayers 65 or older can subtract up to $24,000 of taxable pension and annuity income; ages 55 to 64 can subtract up to $20,000.⁹
Social Security: taxpayers 65 or older can subtract the full benefit amount included in federal taxable income. For ages 55 to 64, the full subtraction is available if AGI stays below $75,000 single or $95,000 joint; above those thresholds, the subtraction is capped at $20,000.⁹
CollegeInvest 529 contributions: deductible up to $26,200 per beneficiary for single filers and $39,200 per beneficiary for joint filers.¹⁰
Prior-year state income tax refund that was pulled into your federal gross income.

Other subtractions exist for certain capital gains on qualifying Colorado investments and other categories spelled out in the Form 104 instruction booklet.

The Deduction Rule

After additions and subtractions you take a deduction, but the choice has to match your federal return. Standard federally means standard on Colorado; itemized federally means itemized on Colorado.¹¹ Colorado has no personal exemption. Whatever is left after the deduction is multiplied by 4.40%.

Credits That Reduce the Bill

Credits come off the tax dollar for dollar, and several Colorado credits are refundable, meaning they can generate a check even if your tax is zero.

Earned Income Tax Credit

Colorado’s EITC is a refundable percentage of the federal EITC you claimed. For the 2025 tax year the state credit is 50% of the federal amount.¹² The percentage has changed before, so confirm it for the year you’re filing.

Child and Dependent Care Expenses Credit

If you paid for child or dependent care so you could work, Colorado offers a credit tied to the federal child and dependent care credit. Starting with the 2026 tax year, the Colorado credit is calculated on the full federal credit you were eligible for, even if a low federal tax liability stopped you from using all of it federally. The Colorado version is refundable.¹³

PTC Rebate and Disability Assistance Credit

The Property Tax/Rent/Heat rebate helps low-income seniors with housing and energy costs. You can qualify as a full-year Colorado resident who is 65 or older, or a surviving spouse 58 or older.¹⁴ Beginning with the 2025 tax year, individuals with disabilities who previously qualified for the PTC claim a separate benefit instead, the Disability Assistance Credit (DAC), which goes directly on your income tax return rather than through the PTC application. DAC amounts run from $400 to $1,200 depending on income and filing status, with a federal AGI limit of $20,000 single or $32,000 joint.¹⁵ If you qualify as both a senior and a person with a disability, you can only claim one per year.

TABOR Refund

Colorado’s Taxpayer’s Bill of Rights requires the state to return excess revenue, and you claim your share as a state sales tax credit on Form 104 (or on the PTC application). It isn’t a separate check; it’s folded into your regular refund. For the 2025 tax year the refund runs from $19 to $59 for single filers and $38 to $118 for joint filers, with the amount tied to AGI.¹⁶ Amounts change year to year with state revenue. No return, no TABOR money.

Deadlines, Extensions, and Estimated Payments

Form 104 is due April 15, the same day as the federal return. Colorado grants an automatic six-month extension to October 15 with no paperwork. The catch is that the extension covers filing only, not payment. To avoid penalties, you must pay at least 90% of your tax liability by April 15.¹⁷ If you’re not sure what you’ll owe, estimate high and send that by the original deadline.

If your Colorado tax after withholding and credits will be $1,000 or more, you’re expected to make quarterly estimated payments using Form DR 0104EP.¹⁸ That mostly affects self-employed workers, freelancers, and landlords. The quarterly due dates:

First quarter: April 15
Second quarter: June 15
Third quarter: September 15
Fourth quarter: January 15 of the following year

If a date falls on a weekend or holiday, it moves to the next business day.¹⁸ Short installments trigger their own penalty, calculated on the amount you underpaid.

How to File and Pay

The Department of Revenue runs a free e-file service called Revenue Online that handles Form 104 at no cost and doesn’t require you to set up an account first.² Most commercial tax software supports Colorado e-filing as well. Electronic returns produce fewer errors and faster refunds. Paper filers mail returns with payments to one address and refund or zero-balance returns to another; the correct addresses are printed in the Form 104 instruction booklet.

For paying, electronic funds withdrawal during e-filing is the simplest route. You can also pay through Revenue Online or mail a check or money order to the Colorado Department of Revenue with your Social Security number and the tax year written on it.

Refunds from e-filed returns typically arrive in three to five weeks. Paper returns can take up to three months.¹⁹ The “Where’s My Refund” tool on the CDOR website tracks the status.

What Late Filing or Paying Costs

The late-filing or late-payment penalty is the greater of $5 or 5% of the unpaid tax, plus 0.5% for each additional month the balance stays open, capped at 12% of the tax due. Interest runs on top. For calendar year 2026, CDOR charges 11% annually on unpaid balances, or 8% if you’ve set up a qualifying payment arrangement.²⁰ If you can’t pay the full balance by April 15, file the return anyway. That alone keeps the late-filing penalty from stacking on top of the late-payment penalty.

Fixing a Return After You’ve Filed

If you spot an error later, correct it on Form DR 0104X, the Amended Colorado Income Tax Return, using the version that matches the year you’re fixing.²¹ Enter the corrected totals rather than just the differences, and file through Revenue Online when possible to cut down on processing errors. The deadline for claiming a refund on an amendment is generally four years from the original due date, or three years from the date you last paid tax for that year, whichever is later. If a federal change forced the amendment, file the Colorado version promptly so the refund window doesn’t close.

Documents to Have Ready

Your completed federal Form 1040 is the single most important document, because so many lines on Form 104 pull directly from it. Beyond that, gather:

W-2s for wages and 1099 forms for interest, dividends, freelance income, and retirement distributions (1099-R).
Schedule K-1 forms for partnership or S-corporation income.
1099-R forms and your age as of December 31 if you’re claiming the retirement subtraction.
Property tax, rent, and heating cost records if you’re applying for the PTC rebate or DAC.
Child care provider name, address, tax ID, and amount paid.
CollegeInvest statements showing 529 contributions for the year.

Keep your return and supporting documents for at least four years, which covers Colorado’s standard audit window. Seven years gives a wider cushion if income was substantially underreported.

1
Department of Revenue – Taxation. Individual Income Tax Guide
2
Department of Revenue – Taxation. File Individual Income Tax Online
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Colorado Department of Revenue. Individual Income Tax Filing Requirements
4
Colorado Department of Revenue. DR 0104PN – Part-Year Resident/Nonresident Calculation Schedule
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Colorado Department of Revenue. Colorado Form 104PN – Part-Year Resident/Nonresident Tax Calculation Schedule
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Department of Revenue – Taxation. DR 1059 – Exemption from Withholding for a Qualifying Spouse of a U.S. Armed Forces Service Member
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Department of Revenue – Taxation. Individual Income Tax Frequently Asked Questions
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Colorado Department of Revenue. Income Tax Topics – State Income Tax Addback
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Department of Revenue – Taxation. Income Tax Topics: Social Security, Pensions and Annuities
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CollegeInvest. Understanding the Colorado 529 Tax Deduction
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Colorado Department of Revenue. 2025 Colorado Individual Income Tax Filing Guide
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Department of Revenue – Taxation. Income Tax Topics: Earned Income Tax Credit
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Department of Revenue – Taxation. Income Tax Topics: Child and Dependent Care Expenses Credit
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Department of Revenue – Taxation. DR 0104PTC – Colorado Property Tax/Rent/Heat Rebate Application
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Department of Revenue – Taxation. Disability Assistance Credit
16
Department of Revenue – Taxation. TABOR
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Colorado Department of Revenue – Taxation. Individual Income Tax Due Dates and Filing Extension
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Department of Revenue – Taxation. Individual Income Tax Estimated Payments
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Department of Revenue – Taxation. Refund
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Colorado Department of Revenue. Tax Topics: Penalties and Interest
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Department of Revenue – Taxation. DR 0104X – Amended Individual Income Tax Return