When Are S Corporation Taxes Due in 2026?

S corporations give small business owners the best of both worlds — corporate liability protection and pass-through taxation. But with those benefits come specific IRS filing obligations that can easily trip up even the most diligent entrepreneurs. Missing a deadline could lead to late filing penalties, lost S corp status, and unnecessary stress at tax time.

To help you stay on track, we’ve outlined everything you need to know about S corporation tax deadlines for 2026 — including filing dates, payment requirements, state deadlines, and what to do if you fall behind.

Key Highlights

• S corporation tax returns (IRS Form 1120-S, U.S. Income Tax Return for an S Corporation) for calendar-year businesses are due March 17, 2026 (since March 15 falls on a Sunday).

• Filing extension: Submit IRS Form 7004, Application for Automatic Extension of Time To File Certain Business Income Tax, Information, and Other Returns, to extend your due date to September 15, 2026.

• Payments are still due by the original March 17 deadline — even if you file an extension.

• State deadlines often mirror the federal schedule but vary; some, like California, extend to October 15.

• Late filings can trigger IRS penalties of up to $245 per shareholder per month.

• 1-800Accountant, America's leading virtual accounting firm, helps small business owners stay compliant with personalized filing reminders and year-round expert support.

Why S Corporation Tax Deadlines Matter

S corporations are pass-through entities — income and losses flow through to shareholders’ individual tax returns. However, the business itself must still file an informational return, Form 1120-S, with the IRS and issue Schedule K-1 forms to each shareholder.

Missing this filing can lead to costly penalties and even jeopardize your S corp election. For instance, one 1-800Accountant client (a two-member consulting firm) once overlooked their filing deadline by six weeks and faced over $2,600 in combined late-filing fees. Their designated 1-800Accountant team helped them secure penalty abatement and rebuild compliance processes for the next year — proof that proactive support matters.

Form 1120-S requirements explain that every S corp must include Schedule K-1s for shareholders. When you partner with 1-800Accountant’s business tax services, we help ensure those forms are filed accurately and on time.

Federal S Corporation Filing & Payment Deadlines for 2026

Standard Deadline (Without Extension)

By IRS rule, S corp tax returns are due the 15th day of the third month after the end of the tax year. For a calendar year S corporation, that means March 17, 2026, since March 15 is a Sunday.

While the 2026 S corp tax deadline is March 17 for a calendar year businesses, it's different for businesses that adhere to a different schedule. If your fiscal year ends on a date other than December 31, your Form 1120-S due date 2026 is likely due three months later.

Extension Deadline

If you need more time to file, submit Form 7004 to automatically extend your S corp return by six months, moving your deadline to September 15, 2026.

Remember — this extension only covers filing, not payment. Any taxes owed (such as built-in gains or excess net passive income tax) must be paid by March 17, 2026 to avoid interest and penalties.

Payment Deadline & Estimated Taxes

Although most S corporations don’t pay federal income tax directly, they may still owe certain entity-level taxes. Shareholders often make estimated tax payments for their share of the income.

Wondering about S corp estimated tax payments 2026? Key 2026 estimated payment dates for shareholders (and any S corp-level tax) are:

• April 15, 2026 – Q1 payment

• June 15, 2026 – Q2 payment

• September 15, 2026 – Q3 payment

• January 15, 2027 – Q4 payment

See the IRS estimated tax calendar for updates, and remember to submit by each deadline to avoid penalties and interest. 

State & Local S Corporation Return Deadlines

Most states align with the federal S corp due date, but some differ:

Always verify your state’s rules or consult a professional before entering a new market. Our CPAs, EAs, and tax professionals manage multi-state filings for clients nationwide, ensuring compliance wherever you operate.

What Happens If You Miss the Deadline

Late Filing Penalties & Interest

There is a penalty for S corp late filing. If your Form 1120-S is late, the IRS assesses $245 per shareholder per month, up to 12 months.

For example, a three-shareholder S corp that’s two months late could owe $1,470 in penalties, even if no tax is due. Interest may also accrue on unpaid amounts.

In severe cases, repeated non-compliance can cause the termination of your S election, forcing you to file as a C corporation.

How to Mitigate or Fix Late Filings

If you’re already behind, it's in your best interest to act fast:

• File immediately to stop additional penalty accrual.

• Request penalty abatement if you have reasonable cause (e.g., illness, natural disaster, or reliance on incorrect IRS guidance).

• Correct late S elections using IRS relief procedures.

• Work with a tax professional who can negotiate directly with the IRS and prepare the necessary documentation.

1-800Accountant routinely assists small businesses with late filings, S corp extension deadlines, and IRS correspondence — restoring compliance efficiently and professionally.

Special Situations to Watch in 2026

Fiscal (Non-Calendar) Year S Corporations

If your S corporation doesn’t follow a calendar year, your due date falls on the 15th day of the third month after your fiscal year ends.

For instance, if your fiscal year closes June 30, 2026, your return is due September 15, 2026.

Newly Elected S Corporations / Late Elections

New S corporations must file IRS Form 2553, Election by a Small Business Corporation, within 2 months and 15 days after formation or the start of the tax year. Missing this deadline can delay your S corp status, impacting your filing schedule. 

Late elections may still qualify for retroactive relief if you meet certain IRS criteria.

Terminated or Dissolved S Corporations

If your S corp dissolves or terminates its election during 2026, you must file a short-year return covering the period from the start of the year to the termination date. 

Doing this ensures that all shareholders report the correct income on their personal returns.

S Corp Tax Timeline for 2026

Tips to Stay Compliant & Avoid Missed Deadlines

Use these tips to stay compliant while avoiding missed deadlines for your S corporation. 

• Use a tax calendar: Sync IRS deadlines with your project management or calendar app and label it as "S corp tax calendar 2026."

• Maintain real-time bookkeeping: Cloud tools and regular reconciliations make year-end filing easier.

• Set reminders for estimated taxes to avoid cash-flow surprises.

• Engage professionals early: Partner with experts like 1-800Accountant to track due dates and optimize deductions.

• Review deductions quarterly: Our S corp deductions list helps ensure you capture every legitimate write-off.

A recent 1-800Accountant client, a small e-commerce owner, avoided over $1,000 in late fees by automating reminders and letting our accountants file their return ahead of schedule — proof that proactive planning pays off.

Next Steps

The 2026 S corporation tax deadline for most calendar-year businesses is March 17, 2026, with an optional extension to September 15, 2026. Staying ahead of these dates protects your business from penalties and preserves your S corp election status.

If you’re unsure about your filing requirements or just want peace of mind, schedule a free consultation with 1-800Accountant. Our CPAs, EAs, and tax professionals will help you plan, file, and stay compliant, so you can focus on growing your business instead of worrying about tax deadlines.