All Colorado State offices will closed Wednesday, June 19, 2024 in observance of Juneteenth. To see a list of State closures, please visit


C Corporation Filing Information

E-File Options

First, complete the federal income tax return you will file with the Internal Revenue Service (IRS). You will use figures or data from your federal return on your Colorado income tax return. The Colorado Department of Revenue offers a free e-file and account service called Revenue Online to file your state income tax. Visit the File Online page for more information.

Extension of Time to File

Calendar year returns are due by  April 15, 2024. If you are unable to file by your prescribed due date, you may file under extension. This will allow you an additional six months to file your return, or until October 15th for calendar year filers. However, the extension to file does not allow you to extend your payment due date. You must pay at least 90% of your tax liability by the original due date of your return and the remainder by the filing extension due date to avoid delinquent payment penalties.

Amending a Return

If an amended return is filed with the IRS, or if the IRS changes the content of the return, an amendment must be filed with Colorado. Use Revenue Online or the DR 0112X to amend the Colorado return. If the Colorado amended return is filed to report an adjustment made by the Internal Revenue Service, a copy of the federal revenue agent’s report must be submitted with the amended return.