March 2026 Business Tax Calendar: S Corps, Partnerships, and Information Returns

If January and February were the warm-up act, March is the main event for many of our business clients here in California. While individual tax season is humming along in the background, this month brings the primary filing deadlines for flow-through entities. For the team here at Christiansen Accounting, this is crunch time for ensuring your partnerships and corporations stay compliant.

Because the standard March 15 deadline falls on a Sunday this year, you get a small grace period until Monday, March 16, 2026. However, we always recommend getting your data to us well before the wire.

Here is your essential checklist for business due dates this month.

March 2: The "Paper" Deadline & Special Industries

While the vast majority of our clients file electronically, the IRS maintains an earlier deadline for paper filings. If you are still handling certain forms manually, this is your cutoff.

Information Returns (Paper Filing)

If you are filing paper copies of Form 1099 (excluding the 1099-NEC which was due earlier) and the transmittal Form 1096, they must be sent today. This deadline also applies to paper filings for Applicable Large Employers (ALE) submitting Forms 1094-C, 1095-C, 1094-B, and 1095-B regarding health coverage.

Additionally, large food and beverage establishments filing paper Form 8027 (Tip Income) must do so by this date. Please note: if you file any of these forms electronically, you generally have until March 31.

Farmers and Fishermen

If you did not pay your estimated taxes by January 15, your 2025 income tax return (Form 1040) is due today to avoid penalties.

Corporate office building representing business tax season

March 16: Partnerships and S Corporations

This is the most critical date of the month for many small to mid-sized businesses. Since March 15 is a Sunday, the deadline moves to today, Monday, March 16.

Partnerships (Form 1065)

Partnerships operating on a calendar year must file Form 1065 today. Crucially, this is also the deadline to issue Schedule K-1s to your partners. They cannot file their personal returns until they receive these documents, so delays here create a bottleneck for everyone involved.

If you need more time, we can file Form 7004 to request an automatic 6-month extension. Remember, an extension to file is not an extension to pay any taxes owed.

S Corporations (Form 1120-S)

Similar to partnerships, S Corps must file their 2025 income tax return and pay any tax due by today. Shareholders must receive their Schedule K-1s by this date as well.

S Corp Elections

Are you looking to change your tax treatment? Today is the deadline to file Form 2553 to elect S Corporation status for the 2026 tax year. If you miss this window, the election generally won't take effect until 2027, unless you qualify for special relief.

Office setting representing tax planning and deadlines

March 31: Electronic Filing Deadline

For those leveraging technology (which we highly encourage), the end of the month serves as the final due date for electronic filing of information returns.

  • Forms 1099 and W-2G: If you file these electronically, they must be submitted to the IRS by today.
  • ACA Forms: Electronic filing of Forms 1094 and 1095 (B and C series) is due.
  • Tip Reporting: Electronic filing of Form 8027 is due.

Standard Rules & Disaster Relief

The Weekend Rule: As noted above, when a due date falls on a weekend or legal holiday, it pushes to the next business day.

Disaster Area Extensions: Living in California, we know that weather events can disrupt business operations. If a geographical area is designated as a federal disaster area, the IRS often grants automatic extensions.

To check if your area is affected, you can verify the current status here:

Navigating partnership and corporate deadlines can be complex. If you have questions about your K-1s or need to file an extension, contact Christiansen Accounting today so we can get you sorted before the deadline passes.

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