If you’ve relied on postmark dates as proof of on-time filings in the past, the United States Postal Service’s recent update has changed how postmark dates are defined and applied. A low-profile update issued by the United States Postal Service (USPS) (FR Doc. 2025-20740) redefines how postmarks are determined. The change has meaningful consequences for taxpayers who still mail tax returns, extensions, payments and other time-sensitive documents. Because the IRS and many state and local agencies continue to treat the postmark as evidence of timely filing, this clarification deserves close attention.
What’s different
Effective December 24, 2025, USPS revised its Domestic Mail Manual to formally defines what a postmark is and and when it’s applied. In the new update, the official postmark date is tied to the first automated processing scan at a USPS facility, not the day the envelope is placed in a mailbox or handed to postal staff. Mail deposited on a deadline may not be processed until the following day, or later, resulting in a postmark after the due date. Manual postmarks and Certificates of Mailing remain available as tools to document timely mailing, so physically taking mail to a USPS location to request a correctly dated postmark is still an option.
While USPS has not changed how mail physically moves through its system, the update clarifies how modern sorting and transportation practices affect postmark timing.
Why this matters
Tax professionals are aware that a mailed return or payment is generally considered timely if it is addressed correctly, sent with sufficient postage, postmarked on or before the filing deadline and left with the USPS by the filing or extension deadline.
Internal Revenue Code §7502 allows the IRS to treat the postmark date as the filing date when a document arrives after the deadline. The problem is that the new USPS definition separates the postmark from the actual act of mailing.
As a result, a client who places a return in the mail on April 15 may still receive an April 16 (or later) postmark if the item is not processed the same day regardless of the actual day of mailing.
How the consequences could affect filers
Returns and extensions: A return mailed by the deadline but postmarked later could be deemed late which opens the door to penalties, interest and disputes that could have been avoided.
Tax payments: Estimated taxes, property taxes, and other mailed payments are particularly vulnerable. Several local treasurers are already advising taxpayers to mail payments early or use online options.
Charitable contributions: For year-end donations, a delayed postmark may impact whether a contribution qualifies for deduction in the intended tax year.
Steps to take now
This change shifts more responsibility onto taxpayers and preparers. Firms should proactively adjust their processes and client guidance by:
- Encouraging earlier or online filing
E-filing eliminates postmark uncertainty altogether. When mailing is unavoidable, certified or registered mail provides stronger documentation. - Using manual proof of mailing
Advise clients to request a manual postmark at the postal counter or obtain a Certificate of Mailing when deadlines are tight.