If you need to change or amend an accepted Colorado State Income Tax Return for the 2024 or previous Tax Year, you need to complete Form 104X. Form 104X is a Form used for the Tax Amendment. You can prepare a 2024 Tax Year Colorado Tax Amendment on eFile.com, however you cannot submit it electronically. In comparison, the IRS requires a different Form - Form 1040X - to amend an IRS return (do not use Form 1040 for an IRS Amendment).
The IRS might send you a notification to change an error on your Return, or you might have discovered an error. If you or the IRS amended or changed one of your IRS Tax Return(s), the IRS will report this to the Colorado Tax Agency, thus you should file a Colorado Amendment within one year.
Function:Prepare only a CO State Return
Function:File a Colorado Tax Amendment
Description:You cannot eFile a CO Tax Amendment anywhere, except mail it in.
Only Option:You need to
complete, sign Form 104X for the appropriate Tax Year. Attach all schedules and other documents (including original and new, corrected forms and schedules) to your amended return - Print, Mail the Form to CO Tax Department to:
Tax Payment with Amended Return
Colorado Department of Revenue
Denver, CO 80261-0006
No Tax Payment with Amended Return>
Colorado Department of Revenue
Denver, CO 80261-0005
Function:For all Tax Years prior to the Current Tax Year, Prepare, Print, Sign and Mail-In - see addresses above - your Tax Amendment as soon as possible. Attach all schedules and other documents (including original and new, corrected forms and schedules) to your amended return. You will also file
an IRS Tax Amendment Form 1040X.
Function:Colorado Refund Deadlines
Description:A. Three years from the due date of the original tax year return, including valid filing extensions.
B. One year from the final determination of the amended federal return or federal change, whichever is later, provided that the allowable refund is not more than the decrease in Colorado tax attributable to the federal change or correction.
C. Two years from the payment of an assessment, provided the amended return raises issues relating only to the prior assessment and the refund does not exceed the amount of tax paid on the prior assessment.
D. Two years from the filing of an amended Colorado return resulting in the payment of additional tax, provided that the current amended return raises issues relating solely to the prior amended return and that the refund does not exceed the amount of the tax payment made as a result of the prior amended return.
Additional Colorado Tax Income Taxes Deadlines
Will I get a bigger tax refund in 2026?
Many taxpayers can expect a bigger tax refund on their 2025 taxes. To help you keep up with soaring inflation, the IRS is making bigger changes than usual that could save you big money on your 2025 taxes, which is the tax return you'll file in 2026.
Take control of your personal life relationships, finances, and taxes: follow the tips on this page and keep up with tax planning for next year. You can use this free Tax Refund Calculator 2025 to get a high-level understanding of your taxes.
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