USPS Postmark Changes Could Affect Tax and Payment Deadlines

When mailing on time could still mean “late”

The U.S. Postal Service is implementing an important change to how postmarks are applied, and it could impact anyone mailing time-sensitive documents, including tax returns, estimated payments, or other deadline-driven correspondence.

Effective December 24, 2025, USPS postmarks no longer reflect the date mail is dropped off or handed to a postal clerk. Instead, the postmark date is the day an envelope is first processed by an automated USPS sorting machine, which could be one or more days after mailing.

Why this matters:
For decades, a postmark has served as legal proof that a deadline was met. Under the new rule, mail that is dropped off on time but processed later could be considered late, potentially triggering penalties or interest.

What businesses and individuals should do:
To avoid issues with tax filings or payments:

• Mail time-sensitive items several days before the deadline
• Visit a post office counter and request a hand-stamped (manual) postmark
• Use certified mail or other trackable services
• When possible, file and pay electronically for immediate confirmation

These changes are part of USPS’s broader Delivering for America initiative, aimed at modernizing operations as letter mail declines and package volume increases.

Questions about your tax deadlines or online tax payment options? Contact your Keiter Opportunity Advisor.

Source:

Federal Register | Postmarks and Postal Possession