Postmarks vs Mailing Dates: What Taxpayers Need to Know

Taxpayers have long relied on postmarks as proof of timely mailing, and that hasn’t changed. The IRS continues to honor the “timely mailing equals timely filing” rule under Internal Revenue Code §7502: if your envelope is properly addressed, has sufficient postage, and is postmarked on or before the due date, your return is considered filed on time. For a full list of filing and payment deadlines, see IRS Publication 509.

What's new? A Subtle Change

What’s new is how USPS transports and processes mail.

According to USPS:

While we are not changing our postmarking practices, we have made adjustments to our transportation operations that will result in some mailpieces not arriving at our originating processing facilities on the same day that they are mailed. This means that the date on the postmarks applied at our processing facilities will not necessarily match the date on which the customer’s mailpiece was collected by a letter carrier or dropped off at a retail location.

In summary, postmarks are applied at processing facilities, not necessarily when you mail or drop off your letter.

Why It Matters

If the postmark date slips past the filing deadline, your filing will be late—even if you mailed it earlier. This nuance is critical for taxpayers who wait until the last minute. Electronic filing avoids this risk because the IRS and state agencies uses the transmission timestamp.

Best Practices for Timely Mailing

To avoid surprises and ensure compliance, consider these steps:

1. Request a Manual Postmark

   • Go to a USPS retail counter and ask for a hand-stamped postmark. This guarantees the date matches the day you mail your item.

   • This is especially important if you’re mailing close to a deadline.

2. Use Certified Mail or Certificate of Mailing

   • Certified Mail provides tracking and proof of delivery.

   • A Certificate of Mailing is inexpensive and serves as official evidence that you mailed the item on a specific date.

3. Avoid Collection Boxes for Last-Minute Filings

   • Dropping mail in a collection box late in the day may delay processing until the next day, resulting in a later postmark.

4. Mail Early

   • Don’t wait until the last day. Mailing early reduces the risk of delays and ensures your postmark is timely.

5. Consider Private Delivery Services

   • If using FedEx, UPS, or another IRS-approved carrier, check the IRS list of designated services. These carriers have their own rules for proving mailing dates.

6. File Electronically When Possible

   • E-filing eliminates mailing uncertainties and provides instant confirmation of submission.