Business tax deadlines 2026: Corporations and LLCs

Author: The Carta Team
Read time: 5 minutes
Published date: March 23, 2026

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

Contents: April 15, 2026: Schedule C (Form 1040)

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

Who must file?

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). A form must be filed for each employee who exercised an ISO.

Good to know:

• This is the deadline for filing by mail; the filing deadline for Form 3921 electronically is March 31 (see below).
• 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)

Who must file?

S corporations must file Form 1120-S. The deadline for C corporations is generally April 15 (see more below).

Good to know:

• This deadline applies to S corporations that use December 31 as the end of their fiscal tax year; check IRS guidelines for deadlines if your fiscal tax year ends on a different date.
• S corps can receive an extension (to September 15, 2026) by filing Form 7004 (Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns) by the regular due date of the return.

March 31, 2026: Form 3921, if filing electronically

Good to know:

• This is the deadline for filing electronically; the deadline for filing Form 3921 by mail is March 2 (see above).

April 15, 2026: Form 1120 (C corps)

Who must file?

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

Good to know:

• This deadline applies to C corps that use December 31 as the end of their fiscal tax year; check IRS guidelines for deadlines if your fiscal tax year ends on a different date.
• C corps can receive an extension by filing Form 7004 (Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns) by the regular due date of the return.

LLC tax deadlines

Tax deadlines for LLCs in 2026 are as follows:

March 16, 2026: Form 1065

Who must file?

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

March 16, 2026: Form K-1

Who must distribute?

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)

Who must file?

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