How a Postmark Delay Could Cause IRS Filing Issues
What Taxpayers Need to Know About the New USPS Postmark Rule
A recent change by the U.S. Postal Service may affect how the IRS treats certain tax documents. Starting December 24, 2025, mail is no longer postmarked when you drop it off. Instead, it is postmarked later, after processing at a regional mail facility.
According to J.D. Supra, “That may sound minor, but for tax filings, deadlines matter. The IRS often relies on the postmark date, not the date you mailed something, to decide whether your paperwork was filed on time.”
Why Postmarks Matter on Your Tax Return
The IRS treats a mailed tax return or payment as on time if it has a postmark dated on or before the deadline. This is part of the longstanding “mailbox rule” used in tax law.
With the new USPS rule taking effect December 24, 2025, that postmark may not match when you actually handed it to the Postal Service. Instead, it may reflect a later date when it was first processed by sorting machines.
This could lead to problems such as:
A tax return being treated as filed late,
Interest or penalties because the IRS sees a late postmark, or
Extra time spent proving you mailed it on time.
Before vs. After the Postmark Change
Hypothetical Taxpayer Scenario
How to Protect Yourself When Mailing Tax Documents
If you must mail something to the IRS, here are ways to make sure you have strong proof of when you mailed it:
Go to the Post Office Counter
Ask for a manual hand-stamped postmark that shows when you handed it over.
Buy your postage at the counter so the imprint shows the correct acceptance date.
Use Certified or Registered Mail
These options give you a dated receipt.
This receipt can help show the IRS when you mailed your forms.
File or Submit Electronically
E-filing or online payment has a built-in timestamp.
Electronic filing eliminates uncertainty about postmarks.
Charitable Giving Impact
While the focus here is on tax return timing, this postmark change also affects year-end charitable deductions. Under IRS rules, a mailed donation counts for a tax deduction in the year shown by the postmark. But because postmarks may now be applied later, a gift sent on Dec. 31 could be postmarked in January and count for the next tax year instead.
To protect your deduction, consider:
Asking for a hand-stamped postmark
Using certified mail or an in-office postmark
What This Means for You
The bottom line is that even something as simple as mailing a tax return or payment could now carry a greater risk of an unintended late date stamp. If you anticipate mailing time-sensitive tax documents, take one of the extra steps above to protect your filing deadline.
If you have questions about how this change might affect your specific tax situation, reach out to our team before sending anything by mail to the IRS.