When you mail important tax documents,  like your federal return or an estimated tax payment, the date printed on the envelope matters. For decades, taxpayers have relied on the U.S. Postal Service (USPS) postmark date to meet IRS filing and payment deadlines under the “timely mailing = timely filing/paying” rule found in federal tax law (Internal Revenue Code Section 7502).

Effective December 24, 2025, USPS updated how postmark dates are determined, impacting how mailed tax filings are evaluated by the IRS and other agencies.

What’s Changing With USPS Postmarks

Under the new USPS rule added to the Domestic Mail Manual (DMM §608.11), most machine-applied postmarks will now reflect the date your mailpiece is first processed at a USPS sorting facility, not necessarily the day you dropped it into a mailbox or handed it to a carrier.

Historically, most postmarks were applied nearer to the point of mailing. The new rule makes clear that postmarks generally indicate when mail reaches a processing center,  which could occur a day or more after mailing.

Why This Matters for Your Tax Filing

Under federal tax rules, a tax return or payment is considered timely if the U.S. postmark date is on or before the due date, even if the IRS receives it later. That’s the “timely mailing = timely filing/paying” mailbox rule in IRC Section 7502.

With the USPS change, a piece of mail dropped in a curbside mailbox on April 15 might be postmarked April 16 or later if it reaches a sorting hub afterward. That later postmark could mean the IRS considers your filing or payment late, even if you mailed it by the deadline.

How to Protect Your Filing Deadline

Here are practical steps to avoid issues with mailed tax returns or payments:

  • Request a manual postmark at the USPS counter: Ask a postal employee to hand-stamp your envelope when you present it for mailing. This increases the chance the date printed reflects when the USPS accepted your mailpiece. 
  • Use Certified or Registered Mail: The receipt stamped by USPS when you mail the item shows the date the post office accepted it,  and under IRC §7502, that date can also be used as evidence of timely mailing. 
  • Consider electronic filing and payment: E-filing with electronic payment is the most reliable way to ensure your return and payment are submitted on time without relying on postal delivery dates. Avoid waiting until the deadline day. Filing and paying a few days early can help prevent issues caused by unexpected delays, office closures, illness, or other unforeseen circumstances. 

The USPS rule change doesn’t mean you can’t mail your tax documents, but it does mean you can no longer assume a drop in a mailbox guarantees a postmark on the same day. If you’re mailing items close to the deadline, consider using postal services that verify acceptance dates, or file electronically when possible.