Introduction
Calendar-year S corporations must file their 2025 federal return (Form 1120-S) by March 16, 2026. A timely extension moves that date to September 15, 2026.
This guide is for Australian businesses and owners with U.S. S corporation obligations. U.S. federal deadlines run separately from Australian and U.S. state requirements, so one date never covers all three.
A missed date can cost hundreds of dollars per shareholder per month, even when no tax is owed. Below, we cover Form 1120-S, the Form 7004 extension, payment rules, and Schedule K-1 delivery.
Key Takeaways
- Calendar-year deadline: March 16, 2026; extended deadline: September 15, 2026.
- Form 7004 is due by March 16 and extends filing, not payment.
- Fiscal-year filers use the 15th day of the third month after year-end.
- Late filing can trigger penalties even with zero tax due.
What Is the S Corp Tax Filing Deadline for 2026?
Calendar-year S corporations file the 2025 Form 1120-S by March 16, 2026. The usual March 15 date falls on a Sunday, so the deadline moves to the next business day, as the Form 1120-S instructions confirm.
Form 1120-S and Schedule K-1
Form 1120-S is the primary federal return. The corporation also prepares a Schedule K-1 for each shareholder and furnishes it by the same date, or by the extended date with a timely extension.
The deadline falls before the individual filing deadline because shareholders need K-1 figures to report their share of income, deductions, and credits on personal returns.
No Activity Still Means a Return
The instructions give no exemption for inactive corporations. If the S election is in effect, a return is required, even with little activity or no taxable income.
Entity-level tax is not always zero either. Certain built-in gains and passive income can still be taxed at the corporate level.
Fiscal-Year Corporations
An S corporation with an approved fiscal year generally files by the 15th day of the third month after its tax year ends.
For example, a fiscal year ending June 30 gives a due date of September 15. Confirm any such date against the Form 1120-S instructions, because short years and dissolutions follow their own rules.
Other Deadlines Differ
State income tax, franchise tax, payroll tax, and Australian reporting dates may follow different rules. Do not assume they match the federal date. California, for instance, uses its own Form 100S.
Australian tax residents must also declare foreign income on their Australian return, according to the Australian Taxation Office.
One eligibility point matters for Australian owners. S corporations cannot have direct nonresident-alien or corporate shareholders, so an Australian company cannot hold shares directly.
How Does the S Corp Tax Extension Work?
An S corporation requests an automatic extension by filing Form 7004 by the original deadline, March 16, 2026, for calendar-year filers. A timely, valid request generally moves the filing deadline to September 15, 2026.
Three Dates Not to Confuse
| Date | What it is |
|---|---|
| March 16, 2026 | Original Form 1120-S deadline |
| March 16, 2026 | Deadline to submit Form 7004 |
| September 15, 2026 | Extended Form 1120-S and K-1 deadline |
Disaster relief can shift these dates. For example, an IRS notice postponed certain deadlines to September 28, 2026 for taxpayers affected by San Carlos Apache Tribe storms. That relief is not nationwide.
What Form 7004 Requires
- Name, EIN, and address
- Form code 25 for Form 1120-S
- Tax period
- Tentative tax, payments and credits, and balance due
Incorrect identifying details can invalidate the extension. The Form 7004 instructions set out the conditions.
Payment Is Separate
An extension gives more time to file, not more time to pay. If the corporation owes entity-level tax, estimate and pay it by March 16, 2026. Interest keeps running on unpaid tax regardless of the extension.
A Simple Workflow
- Close the books for 2025.
- Estimate any entity-level tax.
- Submit Form 7004 and pay any balance.
- Save the IRS acceptance or proof of mailing.
- Complete Form 1120-S and the K-1s before September 15, 2026.
Notes for Australian-Based Filers
Australian-based filers should e-file where possible. U.S. mailing protection does not extend to documents sent through another country's postal service.
Some corporations that operate and keep their books outside the U.S. may qualify for a different rule, with a sixth-month due date. Australian ownership alone does not qualify.
What Happens If an S Corp Misses the Filing Deadline?
Penalties can apply even when no regular federal income tax is due. The 2025 Form 1120-S instructions set the amounts for returns due in 2026.
Penalty Exposure
- $255 per shareholder per month (or partial month) late, up to 12 months
- If tax is due, an added 5% of unpaid tax per month, up to 25%
- Late payment: generally 0.5% of unpaid tax per month, capped at 25%
- Late or incorrect K-1: $340 per K-1, unless reasonable cause applies
- Interest on unpaid tax continues until paid
For example, a three-shareholder corporation filing four months late faces a base penalty of $255 × 3 × 4 = $3,060.
Effect on Shareholders
Shareholders owe tax on their share of income whether or not it was distributed. Late K-1s can force them to estimate figures, delay filing, or amend later with Form 1040-X. Shareholders who spot errors should request a corrected K-1 from the corporation.
Steps After a Missed Deadline
- File the return as soon as possible.
- Pay what you can to limit interest and late-payment charges.
- Keep records explaining the delay.
- Check whether penalty relief applies.
The IRS considers reasonable cause relief based on ordinary care, the facts, and supporting evidence. First Time Abate can also cover S corporation failure-to-file penalties, subject to a clean three-year history. Relief is never guaranteed.
How to Prepare for the 2026 S Corp Filing or Extension Deadline
Start with a checklist:
- Reconciled books, plus bank and credit-card statements
- Payroll records
- Fixed-asset and depreciation details
- Shareholder ownership changes
- Distributions and shareholder loans
- Prior-year returns
- Data for each Schedule K-1
Also confirm these points:
- Whether the corporation uses a calendar or fiscal year
- Whether Form 7004 was accepted
- Whether US state or Australian filings need their own extensions
What to Keep
Keep these records on file:
- Filed return and Form 7004
- Payment confirmations and e-file acceptance records
- K-1 delivery records and workpapers
The IRS generally expects supporting records to be kept for three years from the later of each shareholder's return due date or filing date.
Getting Support
Australian businesses managing U.S. S corporation obligations can use VJM Global's accounting, bookkeeping, and tax compliance support. The team coordinates accurate year-end records and timely filings with U.S.-compliant professionals.
Frequently Asked Questions
What is the extended due date for an S Corp?
For a calendar-year corporation with a timely Form 7004, the extended deadline is generally September 15, 2026. IRS disaster relief or holiday adjustments can change this.
What is the late filing penalty for an S corporation?
Generally $255 per shareholder for each month or partial month late, up to 12 months. It can apply even when no tax is owed.
What is the S Corp tax filing deadline for 2026?
Calendar-year corporations file Form 1120-S by March 16, 2026. Fiscal-year corporations file by the 15th day of the third month after year-end.
Does an S Corp extension give more time to pay taxes?
No. It extends the time to file only. Unpaid tax continues to accrue interest and late-payment charges.
Which form is used to request an S Corp tax extension?
Form 7004, using code 25 for Form 1120-S. File it by the original Form 1120-S deadline.
