Dropped Off Doesn’t Mean Filed: How the New USPS Rule Could Affect Your Tax Deadlines

Summary: The USPS now determines official postmark dates based on when an item is first processed at a sorting facility, not when it is dropped off, which means mailed tax returns and payments could be considered late. To avoid penalties, taxpayers should file and pay taxes electronically whenever possible and allow extra lead time for any required paper submissions.

Effective Dec. 24, 2025, the U.S. Postal Service (USPS) formally updated how it defines and applies postmarks on mailed items. This is especially relevant in the context of mailed tax returns and payments, both in the context of federal and state taxes.

Historically, taxpayers have relied on the USPS postmark as evidence that a return of payment was mailed by the due date. However, the USPS has continued moving away from traditional postmark practices in favor of automated processing and internal date-stamping. The new official postmark date is now the date of the first automated processing operation at a USPS sorting facility, which is not necessarily the date the mail was dropped off at the mailbox or post office.

This change has reduced the reliability of mailed documents as proof of timely filing. Mail is often routed through centralized processing facilities and may not be date-stamped on the day it is mailed or even when it is first received. In some cases, envelopes may not receive a clear or legible postmark at all. As a result, the date a tax return, payment, or response is placed in the mail may no longer be sufficient evidence that a filing was made on time.

Implications of the USPS Postmark Change on Federal Tax Filings

The Internal Revenue Service (IRS) generally uses the postmark date (as defined in Internal Revenue Code Section 7502) as the official date that a tax return or payment is “timely filed.” Because the new postmark may lag behind the drop-off date, returns and payments that are mailed on the deadline might end up with a postmark after the due date. This change raises the risk of filings and payments being treated as late.

Late returns and payments can trigger:

• Failure-to-file or failure-to-pay penalties
• Interest charges
• Potential loss of certain elections that are tied to filing dates

To mitigate these risks, all filings and payments should be completed electronically where possible. This is also the safest and most secure way to file and pay.

There are a variety of ways to pay electronically, which include direct debits from your bank account, paying securely on the IRS website, or utilizing EFTPS when applicable.

Implications of the USPS Postmark Change on State Tax Filings

These changes also create increased risk when submitting state and local tax returns, responding to notices, or managing audits or assessments. State taxing authorities may treat mailed items as late if their recorded receipt date falls after a statutory deadline, even when the item was mailed earlier. Resolving disputes over mailing dates can be time-consuming and may not always be successful. In addition, mail delivery delays increase the likelihood that state notices are received with little or no time remaining to respond, which can lead to penalties, interest, or other adverse consequences that could otherwise be avoided.

To reduce these risks, all filings, payments, and communications with state taxing authorities should be completed electronically whenever possible, either through practitioner email submissions or official state tax portals. Electronic filing provides immediate confirmation of submission and creates a clear, time-stamped record of compliance. What’s more, establishing and maintaining online access to state tax accounts allows for real-time monitoring of notices, balances, and deadlines.

Paper Filing Considerations

For filings or correspondence that cannot be submitted electronically and must be mailed, additional lead time will be required. Important considerations include:

• Taxpayers should expect to receive specific advance deadlines for any required paper filings from their tax advisor so the advisor can physically present the materials at the post office and obtain an official date stamp before the applicable due date.
• For items that must be mailed, it’s important to utilize services like certified mail (ensuring the certified mail is accurately stamped with the drop off date with return receipts), registered mail, and/or private delivery services (e.g., FedEx or UPS). Also, maintaining USPS and other tracking documentation is important for proof of delivery.

If you need assistance setting up an online IRS or state tax account, navigating state portals, or evaluating your state and/or federal tax filing options in light of these changes, please contact your KSM advisor or fill out the form below.