General

What taxpayers need to know before mailing returns or payments

What the New USPS Postmark Rule Means for Your Tax Filing

A recent update from the U.S. Postal Service is changing how postmarks are assigned—and it may impact whether your tax return or payment is considered “on time.” Because the IRS and many states rely on the postmark as proof of timely filing, this shift could affect taxpayers who still rely on mailing important documents close to the deadline.

What Changed?

As of late 2025, the USPS now defines a postmark as the date of the first automated processing operation. This means the postmark is no longer tied to the moment you drop your envelope in a mailbox or hand it to a postal clerk. If your mail isn’t processed until the next day—or later—the postmark will reflect that delay.

Manual postmarks and Certificates of Mailing are still available, but they must be specifically requested at the post office.

Why This Matters for Taxpayers

Under IRS rules, if a return or payment arrives after the deadline, the postmark determines whether it was mailed on time. With the new USPS definition, a document mailed on April 15 could receive an April 16 postmark if processing is delayed, potentially triggering:

• Late-filed returns
• Late payment penalties
• Year-end charitable donations being counted in the wrong tax year

Even if you mailed something on time, the automated postmark may not reflect that.

How This Could Affect You

This change is especially important for anyone who:

• Mails paper tax returns
• Sends estimated payments by mail
• Makes year-end charitable contributions
• Relies on the “mailbox rule” for timely filing

Tax professionals nationwide are preparing for more disputes around mailing dates, and many local tax offices are already urging residents to mail items earlier or switch to electronic options.

What You Can Do to Protect Yourself

To avoid unexpected penalties or delays, consider the following:

• File electronically whenever possible. E-filing eliminates postmark risk entirely.
• Mail early. Don’t wait until the deadline—give your documents time to be processed.
• Request a manual postmark or Certificate of Mailing if you must mail close to a deadline.
• Keep documentation. Save receipts, tracking numbers, and any USPS confirmations.

The Bottom Line