Filing Your 2021 Colorado State Income Taxes

Filing Your 2021 Colorado State Income Taxes
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If you are a taxpayer getting ready to file an income tax return in Colorado, you'll want to know what forms you need, where and how to file them and how much you can expect to be taxed.

Who Must File Colorado Income Taxes?

Any individual residing in Colorado or earning income from a Colorado-based source who is required to file a federal income tax return must file a Colorado individual income tax return.

All full-year and part-time residents of Colorado and nonresidents who have income from Colorado must file a Colorado income tax return if they had taxable income during the tax year.

Colorado residents or those who earn income from a Colorado source who are not U.S. citizens will file as a full-year, part-year or nonresident depending on how long they reside in Colorado during the current tax year.

The state of Colorado defines residency as someone who has made a home in Colorado or who has moved there intending to do so. So, even if you reside in a home outside of Colorado for part of the year, you must file a state income tax return in Colorado.

The state income tax will be prorated for nonresidents and partial-year residents, so only income received in Colorado will be subject to tax.

What Are the Forms to Use?

Any taxpayer in Colorado will want to view Book 104 from the Colorado Department of Revenue. There is an additional document available for topics concerning part-year residents and nonresidents.

These helpful guides share general information, as well as the Colorado state tax forms, schedules and worksheets you will need to file your individual income tax return.

  • Form DR 0104 is the personal income tax return form for all individuals, regardless of residency status.
  • Form DR 0104PN is an additional form for part-year and nonresidents to be included with the DR 0104 for calculation/proration of taxes.

Additional forms and schedules can be found on the Colorado Department of Revenue website. There are dedicated pages for retirees, active-duty service members and those filing for a deceased family member, among other tax situations. Through these pages, you can find specific information to ensure you submit all required forms with your Colorado state income tax return.

What Is the Tax Rate in Colorado?

As of the 2021 tax year, Colorado is one of just nine states with a flat rate for individual income tax. Beginning in 2020 with the passage of Proposition 116, Colorado's flat income tax rate is now ​4.55 percent​, regardless of income.

Taxes are calculated for an individual based upon the amount of taxable income subject to federal income tax by the Internal Revenue Service (IRS). Colorado's flat tax of 4.55 percent is applied to an individual's federal taxable income after adjusting for state additions and subtractions.

What Are the Filing Deadline and Extension Process?

Colorado state tax returns must be postmarked or received by ​Monday, April 18, 2022​. Note that while the IRS is giving an automatic federal extension to Colorado wildfire victims until ​May 16, 2022​, the state revenue department hasn't announced a similar provision for state income tax returns.

All taxpayers in Colorado are eligible for an automatic extension to file with form DR0158-1. An extension to file your return is not an extension to pay. At least ​90 percent​ of a taxpayer's tax bill must be paid by the original filing deadline.

The Colorado Department of Revenue publishes a state tax and fee due date guide that may be helpful throughout the year.

What Are the Penalties for Late Filing and Underpayment of Taxes?

If your Colorado state tax income tax return is not filed by the due date, the Colorado Department of Revenue may file a return on your behalf with the information available. The tax filing is deemed sufficient for determining your taxes owed.

Unpaid or underpayment of Colorado taxes will be charged interest ranging from ​3 percent​ to ​6 percent​ of what is owed, depending on how quickly you pay the bill or set up a payment plan.

A penalty of ​5 percent​ of the unpaid tax, or at least $5, will be assessed, along with an additional ​0.5 percent​ of the balance for each month the debt is outstanding. The total penalty cannot exceed ​12 percent​ of the total tax bill.

Additional penalties, as outlined in Colorado's 2021 Individual Income Tax Guide, may be assessed. The penalty may also be waived if certain conditions are met.

For tax liability that remains unpaid, the Colorado Department of Revenue will issue a Notification of Deficiency. You will have 30 days to respond to the notification or pay the bill. Failure to reply or pay will result in further actions outlined on

Where Do I Mail/E-file My Colorado Return?

Free e-filing is available to Colorado taxpayers through Revenue Online. You can e-file without setting up an account, but setting up an account allows you to access more functionality in the portal.

To file paper forms without taxes due, mail the forms to the Colorado Department of Revenue, Denver, CO 80261-0005.

If you are mailing your forms with payment, note that the last digit of the address is different: Colorado Department of Revenue, Denver, CO 80261-0006.

Before mailing forms, review the Colorado Department of Revenue contact guidelines.

How Do I Pay Taxes Due?

You can always mail a check to the Colorado Department of Revenue to pay taxes due. Be sure to include your completed tax form or the payment voucher sent to you with your tax bill.

If you are paying by check but you e-filed, you must submit form DR0900 with a check made payable to "Colorado Department of Revenue." Do not send a copy of the electronic return; just attach the voucher and check and mail it to the Colorado Department of Revenue, Denver, Colorado 80261-0008.

Whether you e-filed or filed a paper return, you may pay taxes due electronically with a debit or credit card, e-check or electronic funds transfer. Each of these methods has a shorter processing timeline and can be competed through Revenue Online.

Where Can I Check My Colorado Refund Status?

You can check your Colorado refund status through Revenue Online. You'll need to know the exact expected refund amount, as well as your Social Security number.

If you receive a legitimate letter from the Colorado Department of Revenue requesting that you confirm your tax return details or verify your identity, this is part of the state's dedication to protecting your identity.

If you have questions about your refund, you may call the Tax Information Call Center at ​303-238-7378​.

What About Colorado State Taxes if You're Self-employed?

Depending on your organizational structure, you may be required to submit estimated tax payments. Review Colorado's Corporate Income Tax Guide to ensure you understand what to file and when.

What About Colorado State Taxes if You're a Business?

Businesses that are required to file a federal income tax return must file a Colorado state income tax return. The corporate tax in Colorado is a flat ​4.55 percent​. Returns are due on ​April 18, 2022​, this year. The Corporate Income Tax Guide is a helpful resource for Colorado businesses.

Rates and dates in this article are correct as of publication. But check for any changes with the Colorado Department of Revenue before you file.