State Tax Day - Current, S.2, Colorado—Multiple Taxes: Guidance Provided on Timely Filing and Postmarks, (Mar 25, 2026)

The Colorado Department of Revenue issued guidance regarding its acceptance of postmarks as evidence of timely filing of tax documents or payments. The guidance notes that adjustments in U.S. Postal Service transportation operations may result in postmarks applied at processing facilities that do not match the date on which the mail was collected by a letter carrier or dropped off at a retail location or collection box. As required by statute, the Department of Revenue will rely upon the postmark to establish the date of filing or payment. Recommendations to ensure that the date of postmark is the date of mailing include manual postmark requests or the use of certified or registered mail services. Electronic options for filing and payment are also available for some tax and fee types.

Timely Filing and Postmarks, Colorado Department of Revenue Division of Taxation, March 2026