Colorado — Personal Income Tax

Colorado requires an individual to file a state income tax return if they meet one of three residency criteria: (1) they were a full-year Colorado resident, (2) they were a part-year resident of Colorado with taxable income during the period of Colorado residency, or (3) they were a nonresident with Colorado-source income—and in any of these cases, they either (a) are required to file a federal income tax return with the IRS for the year, or (b) have a Colorado income tax liability for the year.

The filing requirement is an or test: a Colorado resident who is required to file a federal return must file a Colorado return even if they have no Colorado tax liability. Conversely, an individual in one of the three categories who has a Colorado tax liability must file even if not required to file a federal return.

A Colorado resident is defined as a person who has made a home in Colorado or whose intention is to be a Colorado resident. The Department considers factors including Colorado voter registration, vehicle registration, driver license, school registration, property ownership, and residence of spouse or children in determining residency intent. Additionally, an individual who is not domiciled in Colorado is nonetheless a Colorado resident if they maintain a permanent place of abode in Colorado and spend, in aggregate, more than six months of the tax year in Colorado.

Source: Individual Income Tax Filing Requirements, Colorado Department of Revenue; Colorado Individual Income Tax Guide (2025), Part 1; DR 0104 Instructions

Colorado imposes a flat income tax at a rate of 4.40 percent on the federal taxable income of every individual, estate, and trust for taxable years commencing on or after January 1, 2022. This single flat rate applies uniformly to all income levels regardless of filing status—there are no graduated brackets or marginal rates. The tax is imposed on federal taxable income as determined under Internal Revenue Code section 63, subject to Colorado-specific additions and subtractions.

Temporary reduction for tax year 2024. For the income tax year beginning January 1, 2024 only, the rate was temporarily reduced to 4.25 percent pursuant to Senate Bill 24-228, enacted May 14, 2024. This one-year reduction was required under Colorado's TABOR (Taxpayer's Bill of Rights) refund mechanism to return excess state revenues to taxpayers. The rate returned to 4.40 percent for tax year 2025 and remains at that level unless future TABOR surplus thresholds trigger additional temporary reductions under Colo. Rev. Stat. § 39-22-627.

Historical rates. The 4.40 percent rate has applied for tax years 2022, 2023, and 2025–present (except for the 2024 temporary reduction). Prior rates were 4.55 percent for tax years 2020–2021 and 4.63 percent for tax years 2000–2019.

Future temporary reductions. For state fiscal years commencing July 1, 2024, through June 30, 2034, if excess state revenues remaining after certain property-tax-exemption reimbursements exceed $300 million, the income tax rate may be temporarily reduced in the following income tax year by 0.04 percentage points to 0.15 percentage points, depending on the amount of the surplus. However, if the permanent state income tax rate is 4.25 percent or less, temporary reductions do not take effect unless the TABOR surplus equals or exceeds $2 billion.

Source: Colo. Rev. Stat. § 39-22-104(1.7)(c); Colo. Rev. Stat. § 39-22-627; SB 24-228 (enacted May 14, 2024)

Colorado income tax is imposed on federal taxable income as determined under Internal Revenue Code section 63, modified by Colorado-specific additions and subtractions. Federal taxable income serves as the starting point, and Colorado law requires certain modifications to calculate Colorado taxable income (also called modified federal taxable income). Common additions include state income tax deductions claimed on the federal return and certain qualified business income deductions; common subtractions include pension and annuity income, Social Security benefits, and capital gains (when available based on revenue thresholds).

Source: Colo. Rev. Stat. § 39-22-104 and Colorado Individual Income Tax Guide, Part 2

Colorado individual income tax returns and any payment owed are due April 15 for calendar-year taxpayers. Returns and payments must be postmarked by April 15 if mailed; Revenue Online accepts returns until midnight on the due date. Taxpayers receive an automatic six-month extension to file until October 15, but there is no extension to pay. To avoid penalties and interest, taxpayers who need an extension must pay at least 90% of their tax liability by April 15. If a due date falls on a weekend or legal holiday, the return or payment is due the next business day.

Source: Colorado Individual Income Tax Filing Guide (2025), Part 1

An individual must remit Colorado estimated income tax payments if his or her total Colorado tax liability for the year, less withholding and credits, exceeds $1,000. Estimated payments are due in four equal installments on April 15, June 15, September 15, and January 15 (of the following year) for calendar-year taxpayers. If a due date falls on a weekend or legal holiday, payment is due the next business day. Individuals who receive non-wage income—such as business income, capital gains, interest, dividends, and rents—typically must make estimated payments because tax is not withheld from these sources.

Source: Individual Income Tax Estimated Payments, Colorado Department of Revenue

An individual who is not domiciled in Colorado is nonetheless treated as a Colorado resident for income tax purposes if two conditions are met: (1) the individual maintains a permanent place of abode in Colorado, and (2) the individual spends, in aggregate, more than six months of the taxable year in Colorado. This rule is codified in Colo. Rev. Stat. § 39-22-103(8)(a) and is commonly called the "six-month rule" or "statutory residency rule."

The six-month rule applies even if the person is domiciled in another state. For example, a person domiciled in Texas who leases an apartment in Denver and spends 185 days in Colorado during the tax year (counted in aggregate, not consecutively) is a Colorado resident for that year and must pay Colorado tax on all worldwide income. The rule turns on physical presence plus a fixed abode; mere ownership of Colorado real estate does not, by itself, create a permanent place of abode.

What constitutes a "permanent place of abode"? The Colorado regulation (1 CCR 201-2, Rule 39-22-103(8)(a)) explains that a permanent place of abode may include a house, condominium, apartment, room in a house, or mobile home. The individual need not own the property—leased or rented property qualifies. The Department gives the example of an employee whose out-of-state employer leases an apartment for the employee during a temporary Colorado assignment; that leased apartment is a permanent place of abode for purposes of the six-month test.

Counting days: Days are counted "in aggregate" during the taxable year; they need not be consecutive. A person who spends three months in Colorado in the spring and four months in the fall (aggregating to seven months, or approximately 213 days) exceeds the six-month threshold. The regulation does not define "six months" as a precise day count (e.g., 183 days), but practitioners typically treat more than 183 days as the trigger under analogous state rules; Colorado DOR guidance refers to "more than six months" and Colorado tax.gov materials sometimes cite "more than six months (183 days)."

Important carve-outs and interaction with part-year residency: A person who changes domicile by moving into or out of Colorado during the tax year generally is not considered a statutory resident under the six-month rule, even if that person spends more than six months living in Colorado. Instead, such a person is classified as a part-year resident for the portion of the year during which they were domiciled in Colorado. This distinction is critical for remote workers or snowbirds establishing or abandoning domicile mid-year.

Tax consequence: An individual classified as a full-year resident (whether by domicile or under the six-month rule) is taxed by Colorado on all income from all sources, regardless of where earned. The individual may claim a credit under Colo. Rev. Stat. § 39-22-108 for income taxes paid to other states on the same income, subject to the limitations of that section.

Burden of proof: Under Rule 39-22-103(8)(a), the burden of production and persuasion is on the person asserting a change of domicile or rebutting a presumption of residency.

Source: 1 CCR 201-2, Rule 39-22-103(8)(a); Colorado Individual Income Tax Guide (2025), Part 1

The Colorado six-month statutory residency rule triggers when an individual who maintains a permanent place of abode in Colorado "spends in the aggregate more than six months of the taxable year" in Colorado. Both the statute and the Department regulation use this phrase without specifying a numerical day count. The question that arises in practice is whether exactly 183 days of presence meets the "more than six months" threshold, or whether presence must exceed 183 days.

Plain statutory language. Colo. Rev. Stat. § 39-22-103(8)(a) defines "resident individual" to include "a natural person who maintains a permanent place of abode within this state and who spends in the aggregate more than six months of the taxable year within this state." The Department's regulation, 1 CCR 201-2, Rule 39-22-103(8)(a), echoes this language: the individual must spend "in the aggregate, more than six months of the taxable year in Colorado." Neither the statute nor the regulation converts "more than six months" into a specific day count such as 183, 184, or any other number.

No official day-count guidance. Colorado Department of Revenue publications, including the Individual Income Tax Guide and the Part-Year Residents & Nonresidents publication, repeat the statutory phrase "more than six months" but do not translate it into a specific number of days. The Department's official web pages likewise state only "more than six months."

Comparison to the military servicemember exception. In the same statutory subsection, the Colorado legislature specified an exact day count for a different purpose: under Colo. Rev. Stat. § 39-22-103(8)(b)(I)(A), a Colorado-domiciled servicemember stationed outside the United States may elect nonresident treatment if absent for "at least three hundred five days of the tax year." The legislature's use of a precise day count (305) for the military exception—while using the phrase "more than six months" for the six-month rule—suggests that "more than six months" is not statutorily defined as any particular day count.

Practitioner approach. In a common (non-leap) year of 365 days, six months equals 182.5 days. The plain language "more than six months" would therefore mean more than 182.5 days, which in practice means 183 days or more. However, the question whether exactly 183 days satisfies the "more than six months" threshold, or whether 184 or more days are required, cannot be answered from the text of the statute or regulation alone. No published Colorado case, administrative ruling, or Department guidance definitively resolves this question as of the date of this section.

Practical consequence. An individual who maintains a permanent place of abode in Colorado and is present in Colorado for exactly 183 days during the tax year is in a zone of uncertainty under Colorado law. Conservative practitioners may advise such an individual to file as a full-year resident under the six-month rule. An individual seeking to avoid statutory residency should stay well below 183 days of aggregate presence.

Source: Colo. Rev. Stat. § 39-22-103(8)(a); 1 CCR 201-2, Rule 39-22-103(8)(a); Colorado Individual Income Tax Guide; Income Tax Topics: Part-Year Residents & Nonresidents

Colorado imposes both penalties for failure to file or pay individual income tax when due and interest on late payments. The penalty and interest calculations are separate; both may apply simultaneously to the same unpaid tax.

## Late filing and late payment penalty

For individual income tax, if a taxpayer fails to file a return or pay the tax due by the applicable due date (April 15 for calendar-year filers, or the extended deadline if an extension was granted), Colorado assesses a penalty equal to the greater of $5 or a percentage of the unpaid tax. The percentage is 5 percent plus ½ percent (0.5%) for each full or partial month the tax remains unpaid, not to exceed a total of 12 percent. This means the penalty reaches its 12 percent cap after 14 months (5% initial + 7 × 0.5% = 5% + 3.5% = 8.5% ... continuing to month 14 where 5% + 13 × 0.5% = 12%).

The penalty applies to the net amount of tax due. "Tax" for penalty purposes means the net amount of tax required to be shown on the return, reduced by any amount paid on or before the due date and by the amount of any credit allowable on the return (other than withholding and estimated tax credits).

Example: A taxpayer files a 2025 Colorado individual income tax return on August 15, 2026, reporting $1,000 of tax due with $800 of wage withholding, resulting in a $200 balance due paid with the late return. The return was due April 15, 2026. The late filing/payment penalty is calculated on the $200 unpaid tax: 5% + (4 months × 0.5%) = 5% + 2% = 7%, which equals $14.00. Since $14.00 exceeds the $5 minimum, the penalty is $14.00.

If both a late-filing penalty and a late-payment penalty would apply under Colo. Rev. Stat. § 39-22-621(2)(a) and (b), only the larger of the two is assessed.

## Interest on late payment

Interest accrues on any unpaid income tax from the original due date (determined without regard to any extension of time) until the date the tax is paid. The interest rate is set annually by the Colorado Commissioner of Banking under Colo. Rev. Stat. § 39-21-110.5. The statutory formula is the prime rate as reported by the Wall Street Journal plus three percentage points, rounded to the nearest full percent. The rate is established each July 1 (or the next business day) and becomes effective on January 1 of the following year.

Current and recent interest rates:

• 2026: 11% annual rate
• 2025: 12% annual rate
• 2024: 11% annual rate
• 2023: 8% annual rate
• 2022: 6% annual rate

Interest is computed on a daily basis. If tax is due on April 15, 2026, and paid on August 24, 2026, interest accrues for the 131 days between the due date and the payment date, not over the entirety of 2026. The daily interest rate is the annual rate divided by 365 days (or 366 in a leap year).

Interest applies separately from penalties. A taxpayer who pays late owes both the penalty (up to 12% of the tax) and interest (compounded daily at the statutory annual rate) for the period the tax remained unpaid.

## Discounted interest for early voluntary payment

Under Colo. Rev. Stat. § 39-21-109(1.5), if a taxpayer pays (or agrees to pay) the amount of any underpayment within 30 days of notice of the underpayment, the Executive Director must waive the three-point surcharge above the prime rate, unless the Executive Director determines there has been willful neglect or failure to pay. This means the interest rate during the 30-day payment window can be reduced from "prime + 3" to just "prime" for taxpayers who act promptly after notice—but only if the underpayment was not willful. After the Department issues a notice of deficiency, this early-payment discount no longer applies.

Importantly, this discounted rate applies only to the interest surcharge; it does not reduce the penalty percentage.

## Reasonable cause penalty waiver

Colo. Rev. Stat. § 39-22-621(2)(j) grants the Executive Director authority to waive or reduce any penalties assessed under Article 22 for "good cause," upon making a record of the reasons. The statute does not define "good cause," but the standard is generally understood to include circumstances such as serious illness, natural disaster, reliance on erroneous written advice from the Department, or other events beyond the taxpayer's control that prevented timely filing or payment. The Executive Director may also waive interest imposed in excess of the statutory rate (i.e., interest charged in error).

Penalty abatement is discretionary, not automatic. The taxpayer bears the burden of demonstrating reasonable cause. Interest on the underlying tax liability, however, is rarely waived even when penalties are abated, because interest compensates the state for the time value of money rather than penalizing non-compliance.

## Special rules for estimated tax underpayment

The penalties and interest rules described above apply to the annual return filing and payment obligation. Estimated tax underpayment is treated separately under Colo. Rev. Stat. § 39-22-605. The "penalty" for underpayment of estimated tax is actually an interest charge (not a traditional penalty), calculated at the statutory interest rate imposed under § 39-21-110.5 on the amount of the underpayment for each quarter, for the period of the underpayment. Section 39-22-621(2)(k) confirms that the penalty provisions of § 39-22-621 do not apply to estimated tax required under §§ 39-22-605 and 39-22-606.

## Fraudulent or willful failure to file

For fraudulent or willful failure to file any required income tax return, Colo. Rev. Stat. § 39-22-621(2)(d) imposes a penalty equal to the greater of $75 or 100 percent of the tax due. For a fraudulent, frivolous, or willfully false return, § 39-22-621(2)(e) imposes a penalty of the greater of $150 or 150 percent of the tax due. If any part of a deficiency is due to negligence or disregard of law (but without intent to defraud), § 39-22-621(2)(h) adds 25 percent of the total deficiency.

These enhanced penalties are cumulative with the standard late-filing/late-payment penalty, and all penalties under § 39-22-621(2)(a)–(h) are collected in the same manner as the tax.

Source: Colo. Rev. Stat. § 39-22-621; Colo. Rev. Stat. § 39-21-110.5; Colo. Rev. Stat. § 39-21-109; Tax Topics: Penalties and Interest (Revised October 2025), Colorado Department of Revenue; Interest Rates Set by the Bank Commissioner, Colorado Division of Banking

Colorado allows a nonrefundable credit for income taxes paid to another state, the District of Columbia, or a U.S. territory or possession by a Colorado resident individual, estate, or trust on income derived from sources in that other jurisdiction. The credit reduces double taxation when a Colorado resident earns income in another state that taxes the same income. The credit is subject to strict limitations that ensure Colorado collects tax on income from all sources while providing relief only for income both taxed by the other state and subject to Colorado tax in the same year.

## Who qualifies for the credit

The credit is available only to Colorado residents — individuals, estates, or trusts that are full-year Colorado residents (whether by domicile or under the six-month statutory residency rule in Colo. Rev. Stat. § 39-22-103(8)(a)). A part-year resident may claim the credit only for taxes paid to another state on income derived from sources in that state while the taxpayer was a Colorado resident. A nonresident of Colorado may not claim this credit because nonresidents pay Colorado tax only on Colorado-source income, not on income from other states.

Dual residents. If an individual is a full-year resident of both Colorado and another state for the same tax year (a "dual resident"), that individual may claim credit only for net tax paid to the other state on income derived from sources in the other state, not for taxes paid by the other state on income sourced elsewhere.

## What taxes qualify for the credit

The credit is allowed for income tax or gross receipts tax paid to another state, regardless of the specific name the other state uses for the tax. Colorado Regulation 39-22-108 clarifies that a franchise tax is not a tax on income or gross receipts and does not qualify for the credit. The credit is allowed for taxes paid to another state, the District of Columbia, or a U.S. territory or possession, but is not allowed for income taxes paid to a city (such as New York City) or to a foreign country.

The amount of tax eligible for the credit is the net tax accrued to the other state. "Net tax" means the income tax imposed by the other state (including any alternative minimum tax imposed by the state) minus any income tax credits allowed by that state against the income tax imposed, but not reduced by withholding credits or estimated payment credits. Net tax does not include any recapture of credits the taxpayer claimed in a prior tax year in the other state.

## Credit calculation and limitation: the lesser-of rule

The total credit allowed is the lesser of two amounts:

1. The actual net tax accrued to the other state(s) on income from sources in the other state(s), or

1. The Colorado tax attributable to out-of-state income, calculated as:

> Colorado tax liability × (Federal taxable income from sources outside Colorado ÷ Total federal taxable income for the same year)

This second limitation — often called the "proportional limitation" or "ceiling" — ensures that Colorado collects tax on all income, including the portion earned in other states, but grants a credit only up to the amount of Colorado tax that would otherwise apply to the out-of-state income.

Sourcing. For purposes of determining "federal taxable income from sources outside Colorado," the statute provides that federal taxable income is deemed to be from sources in another state "in the same ratio as the modified federal adjusted gross income is from sources in such state." The regulation explains that "source of income" means the geographical location of the activity that gave rise to the income, not the location from which payment is made. For interest, dividend, and other income from intangible assets (unless arising from the active conduct of a trade or business), the source is deemed to reside with the owner of the intangible asset — meaning a Colorado resident's interest and dividend income is generally Colorado-source income, not out-of-state income eligible for the credit, even if paid by an out-of-state entity.

Multiple states. If a Colorado resident pays tax to multiple states, the total credit for all states combined is limited to the Colorado tax on all out-of-state income (the numerator includes income from all states; the denominator is total federal taxable income). The credit for any single state is limited to Colorado tax multiplied by the ratio of income from that state to total federal taxable income.

## Same-year requirement

The credit is allowed only for taxes that accrue in the same tax year as the Colorado tax year for which the credit is claimed. Colorado follows the accrual method for this credit regardless of the taxpayer's accounting method. If a Colorado resident pays Colorado tax on income from another state that was taxed by the other state in a different tax year, no Colorado credit is allowed. The regulation gives an example: a taxpayer who is a resident of another state makes an IRC § 1031 exchange of property located in the home state for property in Colorado; the other state taxes the gain in year one; the taxpayer becomes a Colorado resident in year two and sells the Colorado property, recognizing the deferred gain. Colorado taxes the gain in year two, but no credit is allowed for the tax paid to the other state in year one because the taxes accrued in different years.

## Documentation and filing requirements

A taxpayer claiming the credit must submit with the Colorado return a copy of the tax return filed with the other state (or so much of the return as is relevant to the determination of the credit). The taxpayer must also provide any additional documentation the Department determines is necessary to verify the credit. The credit is claimed on Colorado Individual Credit Schedule (DR 104CR) and is a nonrefundable credit that reduces Colorado tax but cannot produce a refund.

## Redetermination when actual tax paid differs

If the tax ultimately paid to the other state differs from the amount for which the taxpayer claimed credit on the Colorado return — for example, because an estimated or accrued amount was claimed but the final liability was different, or because the other state later refunds part of the tax — the taxpayer must notify the Colorado Department of Revenue by filing an amended Colorado return to correct the amount of the credit claimed. If the credit must be reduced, the taxpayer will owe additional Colorado tax (plus interest from the original due date); if the credit should have been larger, the taxpayer may claim a refund (subject to the statute of limitations for refunds).

Effective date. The credit in its current form has applied to all taxable years commencing on or after January 1, 1987, under Colo. Rev. Stat. § 39-22-108(1). The statute was substantially amended in 1987 and again in 1988; the 1988 amendment (effective May 29, 1988) added the provision that federal taxable income is deemed to be from sources in another state in the same ratio as modified federal adjusted gross income is from sources in such state.

Source: Colo. Rev. Stat. § 39-22-108; 1 CCR 201-2, Rule 39-22-108; Income Tax Topics: Credit for Tax Paid to Another State (Revised January 2024), Colorado Department of Revenue