Key Deadline Approaching: March 16, 2026 for Partnerships and S Corporations

Tax professionals and business owners should be aware that the federal filing deadline for 2025 Partnership (Form 1065) and S Corporation (Form 1120S) tax returns is Monday, March 16, 2026.

If your business operates as a partnership or S corporation, it is critical to either file the return by this date or submit an extension request to avoid IRS penalties.

This deadline is particularly important for tax preparers managing multiple business clients during the busy filing season.

E-File Rejection Grace Period

The IRS provides a 10-day grace period for e-file rejections.

If a Partnership (Form 1065) or S Corporation (Form 1120S) return is electronically filed on March 16 but rejected, the return can still be considered timely filed as long as:

The issue is corrected,
The return is retransmitted, and
The IRS accepts the return by March 26, 2026.

This rule protects tax professionals who submit returns on time but experience technical rejections during electronic filing.

IRS Disaster Relief Extensions

In certain situations, the IRS grants additional time to file returns and make payments for taxpayers affected by natural disasters. Several states currently have extended deadlines for the 2025 tax filing season.

Missouri — Deadline: March 30, 2026

Businesses and individuals in parts of Missouri affected by severe storms, tornadoes, straight-line winds, and flooding that began March 30, 2025 have until March 30, 2026 to file applicable federal tax returns and make payments.

This relief applies to taxpayers located in counties designated for federal disaster assistance.

Louisiana — Deadline: March 31, 2026

Businesses located in Louisiana impacted by winter ice storms beginning January 22, 2026 have been granted relief until March 31, 2026 to file certain federal tax returns and submit tax payments.

Montana and Washington — Deadline: May 1, 2026

Taxpayers affected by severe weather in the following states also qualify for extended deadlines.

Montana
Businesses and individuals impacted by severe storms and flooding beginning December 10, 2025 have until May 1, 2026 to file federal tax returns and make payments.

Washington
Similarly, taxpayers affected by storms, flooding, landslides, and mudslides beginning December 9, 2025 have until May 1, 2026 to meet their federal filing obligations.

How to Request an Extension (Form 7004)

If additional time is needed to complete a Partnership or S Corporation tax return, taxpayers can request an automatic six-month extension.

To do this, file:

Form 7004 — Application for Automatic Extension of Time to File Certain Business Income Tax, Information, and Other Returns

Filing Form 7004 by March 16, 2026 extends the filing deadline to:

September 15, 2026

Important: Extensions Do NOT Extend Payment Deadlines

A common misconception is that an extension also delays tax payments.

This is not the case.

An extension only provides more time to file the return, not more time to pay taxes owed.

If a partnership or S corporation expects to owe tax, it is recommended to submit payment when filing Form 7004 to avoid:

Late payment penalties
Interest charges from the IRS

Final Reminder for Tax Professionals

With the March 16 deadline approaching, tax preparers should review their client lists to ensure that:

Partnership and S Corporation returns are ready to file, or
Form 7004 extensions are submitted on time.

Proactively filing extensions when necessary helps avoid unnecessary penalties and ensures compliance with IRS filing requirements during the busy tax season.