March 2026 Tax Calendar: Critical Business Deadlines

While April usually gets all the publicity, seasoned business owners know that March is arguably the busiest month in the tax calendar for flow-through entities. If you operate a Partnership or S Corporation, the clock is ticking on your primary tax return.

Beyond income tax filings, March 2026 is also a critical month for finalizing information returns that report health coverage, tips, and other payments. Missing these dates can lead to frustrating penalties, so we have broken down exactly what is due and when.

March 16: The Big Deadline for Flow-Through Entities

Because March 15 falls on a Sunday this year, the deadline for calendar-year Partnerships and S Corporations moves to Monday, March 16. This is effectively the "April 15" for many of our business clients.

Team working on business tax documents

Partnerships (Form 1065)

You must file your 2025 calendar year return (Form 1065) by today. Crucially, you must also provide each partner with their Schedule K-1 (and Schedule K-3 if applicable). Your partners cannot file their personal returns until they receive these forms, so delays here cause a bottleneck for everyone involved.

Need more time? You can request an automatic 6-month extension by filing Form 7004. This extends the filing deadline to September 15, but remember: you still need to provide K-1s to partners as soon as possible so they can manage their own filings.

S Corporations (Form 1120-S)

Similar to partnerships, S Corps must file Form 1120-S and pay any tax due by March 16. Shareholders must receive their Schedule K-1s by this date as well.

To get a 6-month extension, file Form 7004 and pay any estimated tax owed. Filing the extension buys you time for the paperwork, but it does not extend the time to pay taxes owed by the entity.

Making the S Corp Election (Form 2553)

If you have been operating as an LLC or C Corp and want to be taxed as an S Corp for the 2026 tax year, you generally must file Form 2553 by March 16. Filing late usually means the election won't take effect until 2027, so don't sleep on this if you are looking to optimize your tax structure.

March 2: Information Returns (Paper Filers)

The standard February 28 deadline falls on a Saturday, pushing these due dates to Monday, March 2.

Forms 1099 and 1096: If you are filing on paper, government copies of various 1099s (excluding the 1099-NEC which was due earlier) are due now along with the transmittal Form 1096.

ACA Reporting (ALE): Applicable Large Employers (ALEs) filing paper forms must submit Forms 1094-C and 1095-C to the IRS. Other providers of minimum essential coverage must file Forms 1094-B and 1095-B.

Gambling Winnings: Casinos and other payers must file Form 1096 and Copy A of Forms W-2G.

Farmers and Fishermen: If you did not pay your estimated tax by January 15, your 2025 income tax return (Form 1040) is due today to avoid penalties. If you did pay estimates early, you can wait until April 15.

Tax forms close up

March 31: The Electronic Filing Deadline

The IRS encourages e-filing by granting a later deadline. If you file the following forms electronically, you have until March 31 to submit them to the IRS:

  • Forms 1099, 1098, and W-2G: This is the final cutoff for e-filing these information returns.
  • ACA Forms: Electronic filing of Forms 1094-B/C and 1095-B/C.
  • Tip Reporting: Large food and beverage establishments filing Form 8027 electronically.

Other Important March Dates

March 2: Employee Health Coverage Copies

While the IRS filing dates vary, you must provide the actual forms to your employees/recipients by March 2. This applies to Forms 1095-B and 1095-C.

March 16: Payroll & Non-Payroll Withholding

If you are on a monthly deposit schedule, the tax for payments made in February is due.

Extensions for Disaster Areas

If your business is located in a federally declared disaster area, you may have extra time to file. We monitor these announcements closely, but you can also verify your status directly:

Note on Weekends: Whenever a federal deadline falls on a weekend or legal holiday, it automatically rolls to the next business day.

If you are worried about getting your K-1s out on time or need to file an extension, please contact our office immediately. We are here to help you navigate the busy season smoothly.

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