Key Takeaways

• Effective December 24, 2025, the USPS now defines the postmark date as the date of first automated processing, not the mail drop-off date.
• Tax filings and payments must still bear a postmark on or before the due date to be considered timely under Internal Revenue Code (IRC) Section 7502.
• Documents mailed close to filing deadlines may face a higher risk of being considered late due to processing delays.
• Taxpayers can reduce risk by requesting a manual postmark, using Certified or Registered Mail, mailing earlier, or e-filing when available.

 
The U.S. Postal Service (USPS) has implemented an important change to how postmark dates are determined—a change that has significant implications for taxpayers who mail paper-filed tax returns, payments, elections, and other time-sensitive documents.

As of December 24, 2025, USPS determines the official postmark date based on the date of first automated processing. Because federal tax law relies heavily on postmarks to determine whether a filing is timely, this change is especially important for individuals and businesses that continue to rely on traditional mail.

What Is Changing With USPS Postmark Dates?

Under the current USPS rule, the postmark date reflects the date an item first enters automated postal processing, rather than the date the mail item is deposited in a mailbox or dropped off at a post office.

This distinction matters because automated processing may not occur until one or more days after drop-off, particularly during high-volume periods such as tax season or year-end. As a result, a document mailed before a deadline may still receive a postmark dated after the due date.

Why Postmark Dates Matter for Tax Filings

Federal tax law follows the long-standing “timely mailed, timely filed” rule. Under IRC Section 7502, a tax return or other document is considered filed on time if it bears a postmark dated on or before the applicable deadline.

If a document receives a postmark dated after the due date, the IRS may treat it as late—even if the taxpayer mailed it earlier. Potential consequences include:

• Late filing or late payment penalties
• Accrued interest
• Loss of tax elections, refunds, or relief provisions that require timely filing

 
The USPS change increases the importance of mailing methods and timing for paper-filed documents.

Tax Documents Potentially Affected

The revised postmark definition may impact many common tax-related mailings, including:

• Individual, business, and fiduciary income tax returns
• Extension requests
• Estimated tax payments
• Refund claims
• Tax elections and statements with fixed deadlines
• Responses to IRS or state tax authority notices

 
Any filing where timeliness depends on a postmark date deserves added attention.

Frequently Asked Questions (FAQ)

When do the USPS postmark changes take effect?

The USPS postmark rule took effect on December 24, 2025. Mail sent on or after that date uses the date of first automated processing as the official postmark date.

Does this change federal tax filing deadlines?

No. Federal tax deadlines remain the same. However, the change affects how the IRS determines whether a mailed document was filed on time under the “timely mailed, timely filed” rule in IRC Section 7502.

If I mail my tax return on the due date, is it still considered timely?

Not necessarily. If the return is mailed on the due date but is not processed by USPS until after the deadline, the postmark may be dated late. This could cause the IRS to treat the filing as untimely.

How can I ensure my mailed tax documents are considered filed on time?

To reduce risk, taxpayers should:

• Request a manual postmark at a USPS retail counter
• Use Certified Mail or Registered Mail for proof of mailing
• Mail documents several days before the deadline
• Use electronic filing or electronic payment options when available

 
Are Certified Mail and Registered Mail treated differently under IRS rules?

Both Certified Mail and Registered Mail provide strong proof of timely mailing. Under IRS regulations, the certification or registration date is treated as the postmark date if the IRS later questions timeliness.

Does this change apply to state tax filings as well?

Many states follow federal postmark rules, but not all state tax agencies apply them in the same way. Taxpayers should review state-specific guidance or consult their tax advisor to confirm applicable requirements.

Does this affect IRS correspondence and responses to notices?

Yes. Any mailed response to an IRS notice that relies on a postmark date to establish timeliness may be affected. Taxpayers should take extra care when responding close to a deadline.

Moving Forward

The USPS postmark rule changes may appear minor, but it can have meaningful tax consequences. By redefining the postmark as the date of first automated processing, USPS has narrowed the margin for error when mailing time-sensitive tax documents.

Taxpayers should use reliable mailing methods and explore electronic filing options when available. If you have questions about how this change may affect your tax filings or would like guidance on best practices, please contact your KPM advisor.