Colorado Amended Tax Return Tips - CO 104X - John R. Dundon II, Enrolled Agent
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Colorado Amended Tax Return Tips – CO 104X

Colorado Amended Tax Return Tips – CO 104X

When filing a Colorado amended return for individual income tax, these tips will help avoid processing delays.

  • DO NOT include a copy of the 104 (original) return with the 104X. 
  • Include all schedules and supporting documentation. Even when there is no change to the 104CR credit schedule or the 104PN part-year/nonresident form, those forms must be completed again (or you must include copies submitted with the original return). Also attach other schedules or credit certifications to the amended return even if copies were attached to original return. Failure to attach these documents will result in delays and errors.
  • ALWAYS use the form that matches the year you are amending.  For example, if you are amending a 2010 return, use the 2010 104X form.  If you use a form for another tax year, the lines from one tax year to another are different.  Using an incorrect year form will delay processing and cause errors.
  • The 104X form should be the first form seen in any amended packet sent.  Place the 104CR, 104PN and other supporting documents behind the 104X.

File the amended return online through Revenue Online ( 

With Revenue Online, taxpayers Sign Up to get access to their Individual income tax account.  They create their own Login and Password.  Note: It is important to create a Login ID and Password that can be remembered.  Taxpayers will receive an email with an Authorization Code that they must use only the first time they Login to Revenue Online.  The Authorization Code is an extra security precaution.  After you gain access to your account, you may amend your individual income tax return.

  • Click on the ID Number (Social Security Number) in your account, then click on the green All Available tab to see all the tax years you have filed.  Currently, only the 2009 and 2010 returns may be viewed and amended online.
  • See the “I want to…” links in the upper right corner of the screen to Amend a Return.  Returns prior to tax year 2009 must be amended using the Colorado 104X paper return.

For corporations, fiduciaries and partnerships, the same rules apply about using the form that matches the year you are amending and placing the amended return on the top of the packet you submit. DO NOT include the original return in the packet.

For fiduciary and partnership amended returns, use the 105 or 106 form as the amended return.

  • Be sure to CLEARLY MARK the Amended Return checkbox at the top of these forms.
  • The place to indicate “amended return” is at the top of the 105 and 106 forms and it reads:  “Check here if this is an amended return for calendar year 2009 or other tax year.”
  • To ensure the 105 and 106 returns will be noticed in our processing pipeline as amended when we receive them, write AMENDED RETURN in red across the top to draw attention to the return.