S-Corp Return Deadline — March 17
Tuesday, March 17, 2026
S-Corporation Form 1120-S due March 17, 2026 — shareholder K-1s must be issued by this date.
Who must file or pay
All S-Corporations must file Form 1120-S by March 15 (or the next business day). Note: March 15, 2026 falls on a Sunday, so the deadline is Monday March 17.
What you need to know
S-Corporations file Form 1120-S by March 15 each year (March 17 in 2026 due to the weekend). This deadline is one month earlier than individual returns because shareholders need their Schedule K-1 to complete their personal Form 1040.
If your S-Corp is not ready by March 17, file Form 7004 for an automatic 6-month extension to September 15, 2026. The extension applies to filing only — estimated taxes for Q1 remain due April 15 regardless.
The shareholder K-1 deadline is one of the most commonly missed in small business tax. If your K-1 is late, it cascades to your personal return being late. TaxosAgent processes S-Corp returns with full K-1 preparation as part of the Business and Empire tiers.
Failure-to-file penalty: $235 per shareholder per month, up to 12 months. With 2 shareholders, missing by one month costs $470. Missing entirely for a year costs $5,640 for a 2-shareholder S-Corp.
Required forms
- →Form 1120-S
- →Schedule K-1 (for each shareholder)
- →Form 7004 (extension)
A licensed TaxosAgent professional reviews your situation before this deadline — so you maximize savings, not just compliance.
Book a strategy call→Free audit first →guaranteed, or your money back.
Other dates to know
Partnership Return Deadline — March 17
Partnership Form 1065 due March 17, 2026 — K-1s to all partners by this date.
C-Corp Return Deadline — April 15
C-Corporation Form 1120 due April 15, 2026 for fiscal year ending December 31, 2025.
C-Corp Extended Deadline — October 15
Final extended deadline for C-Corporation Form 1120 — October 15, 2026.