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March 2026 Business Tax Calendar: Critical Deadlines for Partnerships and S Corps

While January 31st often feels like the first major hurdle of tax season, March is arguably the busiest month for flow-through entities. If you operate as a Partnership or S Corporation, this is your primary filing season. March 2026 brings a mix of information reporting deadlines, major return due dates, and elections that can shape your tax structure for the coming year.

We have broken down the essential dates below to help you stay compliant and avoid penalties.

March 2: Paper Filing and Industry-Specific Deadlines

While we strongly encourage electronic filing for efficiency and accuracy, the beginning of the month marks the deadline for several paper-filed forms.

Information Returns (Paper)

If you are still filing on paper, you must submit government copies of Forms 1099 and the transmittal Form 1096 for payments made in 2025 (excluding the 1099-NEC, which was due earlier). This also applies to:

  • Gambling Winnings: File Form 1096 along with Copy A of Forms W-2G.
  • ACA Reporting: Applicable Large Employers (ALEs) filing paper Forms 1094-C and 1095-C, and other providers filing Forms 1094-B and 1095-B.
  • Tip Income: Large food and beverage establishments filing paper Form 8027.

Note: If you file these forms electronically, your deadline is extended to March 31 (see below).

Farmers and Fishermen

If you did not pay your 2025 estimated tax by January 15, you must file your 2025 income tax return (Form 1040 or 1040-SR) and pay all tax due by March 2 to avoid penalties.

Business growth concept

March 16: The Big Deadline for Partnerships and S Corps

For calendar-year Partnerships and S Corporations, March 16 is the most critical date on the calendar. Timely filing—or a timely extension—is necessary to generate the K-1s your owners and partners need to file their personal returns.

Partnerships (Form 1065)

You must file the 2025 calendar year return (Form 1065) and provide each partner with their Schedule K-1 (and Schedule K-3, if applicable). If your books aren't quite ready, you can file Form 7004 to request an automatic 6-month extension. This pushes the filing deadline to September 15, though it does not extend the time to pay any tax due.

S Corporations (Form 1120-S)

Similar to partnerships, S Corps must file Form 1120-S and distribute Schedule K-1s to shareholders. If you need more time, filing Form 7004 grants a 6-month extension. However, remember that an extension to file is not an extension to pay; ensure any estimated tax due is paid by this date to mitigate interest and penalties.

S Corporation Election (Form 2553)

If you are an LLC or C Corp and want to be taxed as an S Corporation for the 2026 tax year, you must file Form 2553 by March 16. Filing late generally means the election won't take effect until 2027, unless you qualify for specific relief.

Corporate partnership handshake

March 31: Electronic Filing Deadline

For businesses that leverage technology (as most do), March 31 is the deadline to electronically file several information returns with the IRS. This includes:

  • Forms 1099 and W-2G: E-filing deadline for forms other than the 1099-NEC.
  • ACA Forms: E-filing deadline for Forms 1094-B/C and 1095-B/C.
  • Tip Income: E-filing deadline for Form 8027.

General Rules and Extensions

Weekend & Holiday Rule: When a due date falls on a Saturday, Sunday, or legal holiday, the deadline shifts to the next business day.

Disaster Area Relief: The IRS often provides automatic extensions for taxpayers located in federally declared disaster areas. If your business is in an affected region, check the FEMA and IRS disaster relief pages to see if your deadlines have been postponed.

Stability and growth

Need Help with Extensions?

If you are waiting on late documents or need more time to reconcile your books, don't just let the deadline pass. Filing an extension is a standard and smart strategic move to ensure accuracy. Contact our office immediately if you need assistance filing Form 7004 or preparing your business returns.

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