Business tax deadlines 2026: Corporations and LLCs

Key tax deadlines are coming up in 2026 for LLC and corporation businesses. Here are the dates and IRS forms you need to know.

The deadline to file individual income tax returns for 2025 is April 15, 2026. Tax deadlines vary for startups and other businesses classified as corporations or limited liability companies (LLC).

Here are the key business tax deadlines and important dates for corporations (both C corps and S corps), LLCs, and sole proprietorships for the 2025 tax year:

General business tax deadlines for 2026

November 3, 2025

All business entities that plan to file 10 or more returns in 2026 are required to have their own Transmitter Control Code (TCC) in order to file taxes electronically (e-file). The deadline to request a TCC number via the IRS’s Filing Information Returns Electronically (FIRE) application is November 1, 2025, for the 2026 tax filing year.

February 2, 2026

By February 2, 2026, businesses must provide copy B of Form 3921 to employees. This is also the deadline to file and send Forms W-2 to employees.

February 17, 2026

By February 17, 2026, businesses must send form 1099-B to employees.

Corporation tax deadlines

Tax deadlines for C corporations and S corporations in 2026 are as follows:

March 2, 2026: Form 3921, if filing by mail

Every corporation that had an employee exercise an ISO (incentive stock option) during the tax year must file copy A of Form 3921 (employee ISO exercises).

Good to know:

• This is the deadline for filing by mail; the filing deadline for Form 3921 electronically is March 31.
• Filing late results in penalties, starting at $60 per form (meaning, per employee ISO exercise) if 30 days late and increasing from there.
• A Form 3921 is not required for the exercise of an incentive stock option by an employee who is a nonresident alien and does not receive a Form W-2.

March 16, 2026: Form 1120-S (S corps)

S corporations must file Form 1120-S. The deadline for C corporations is generally April 15.

Good to know:

• This deadline applies to S corporations that use December 31 as the end of their fiscal tax year.
• S corps can receive an extension (to September 15, 2026) by filing Form 7004 by the regular due date of the return.

March 31, 2026: Form 3921, if filing electronically

Every corporation that had an employee exercise an ISO during the tax year must file copy A of Form 3921 (employee ISO exercises).

Good to know:

• This is the deadline for filing electronically; the deadline for filing Form 3921 by mail is March 2.
• Filing late results in penalties, starting at $60 per form if 30 days late and increasing from there.

April 15, 2026: Form 1120 (C corps)

C corporations must file Form 1120 by April 15, 2026.

Company tax reporting requirements

Download our step-by-step guide to understand when and how to report equity-related taxes.

LLC tax deadlines

Tax deadlines for LLCs in 2026 are as follows:

March 16, 2026: Form 1065

LLC and other domestic partnerships must file Form 1065 by March 15, 2026.

March 16, 2026: Form K-1

LLCs and other entities that “pass through” taxes to their partners must distribute a Schedule K-1 Form by March 16, 2026.

Sole proprietor tax deadlines

Tax deadlines for sole proprietors in 2026 are as follows:

April 15, 2026: Schedule C (Form 1040)

Sole proprietors must use Schedule C (Form 1040) to report income or loss from a business they operated or a profession they practiced.

An activity qualifies as a business if:

• Your primary purpose for engaging in the activity is for income or profit.
• You are involved in the activity with continuity and regularity.

Carta's best-in-class software, services, and resources are designed to promote clarity and connection in the private capital ecosystem. By combining industry experience with proprietary data and real customer stories, our content offers expert guidance and clear, actionable insights for companies and investors.