Form 1120-S deadline: the S corporation filing calendar

Quick context: This guide is educational and designed to make the underlying rule easier to operate. Federal, state, and local requirements can depend on entity type, tax year, location, elections, and individual facts, so use the linked primary source and your professional adviser for the final filing decision.

The general due date

Form 1120-S is generally due by the 15th day of the third month after the S corporation's tax year ends. A calendar-year S corporation would normally use March 15; in 2026 that date falls on a Sunday, so the filing deadline is March 16, 2026.

K-1 timing matters to shareholders

The S corporation also furnishes each shareholder a Schedule K-1, and Schedule K-3 when applicable, on the same general timetable. A delayed corporate return can therefore delay the owners' individual returns because the K-1 carries their share of income, deductions, and other tax items.

Extension

Form 7004 is generally used to request an automatic six-month extension for Form 1120-S. As with other business returns, an extension to file does not erase tax or payment obligations that may already be due.

What to finish before the return

Reconcile bank, card, processor, payroll, loan, and equity accounts.
Confirm shareholder ownership changes and dates.
Review shareholder distributions, contributions, loans, and reasonable-compensation records.
Reconcile payroll totals to the general ledger and Forms W-2/941.
Prepare state apportionment and registration information where relevant.

Primary sources

Verify the rule at the source.

IRS — Instructions for Form 1120-S IRS — Publication 509