S-Corp Filing Deadline: September 15

When Is the S-Corp Return Actually Due?

March 15 for a calendar-year S corporation, being the 15th day of the third month after the year closes. Form 7004 extends it six months, to September 15. A fiscal-year company shifts both dates, so a June 30 year end lands on September 15 as its original due date rather than its extended one.

Those are two separate filings by two different filers, and that is where most of the trouble starts.

Does My Personal Extension Cover the Company?

No. Your extension covers your Form 1040. The corporation is a separate taxpayer filing a separate return, and it needs its own Form 7004.

The Tax Court decided this on exactly those facts in a reported opinion, which means it is precedent rather than a one-off. The shareholders of an S corporation applied for an extension for their personal returns and filed those on time within the extended period. The company itself never applied for an extension and filed its Form 1120-S late. The penalty was assessed by computer, and the court held the company liable anyway.

Two arguments the company raised and lost are worth knowing, because they are the arguments most owners reach for. That the shareholders had extended and filed on time did not matter. And that the IRS had apparently excused the same penalty for another year on similar facts did not matter either.

The court also closed a procedural door. A penalty that is automatically calculated by computer does not require a supervisor's written approval before it is assessed, so the approval argument that works against many penalties does not work against this one.

Practice pointer. Ask your accountant a specific question rather than a general one. Not "did we get an extension" but "was a Form 7004 filed for the company, and can you send me the acceptance." Those are different questions and only the second one has an answer you can rely on.

How Much Is the Late-Filing Penalty?

The penalty runs per shareholder, per month, currently $235, for up to twelve months. It is charged on the return being late, not on tax being owed.

• Five shareholders, three months late: $3,525
• Ten shareholders, three months late: $7,050
• Ten shareholders, a full year late: $28,200

Two features make it worse than it first reads. The penalty accrues at the entity level and reaches the shareholders through the entity, so an owner who had nothing to do with the filing pays a share of it. And it is not deductible.

Avoid assuming a company with no income is safe. The penalty is measured by shareholders and months, so a dormant S corporation with four owners accrues it at the same rate as a profitable one.

The Extension Never Extended Time to Pay

Form 7004 extends the time to file. It does not extend the time to pay. An S corporation that owes built-in gains tax or excess net passive income tax owed those by March 15, extension or not, which means interest has been accruing since the spring on anything left unpaid.

There is a second version of this that catches shareholders rather than the company. A K-1 reports your share of the profit whether or not any cash was distributed to you, so a shareholder can owe tax in April on money that is still in the company bank account. That is phantom income, and it is the most common reason a partner discovers the return was late, because the K-1 that would have warned them never arrived.

That catches former C corporations most often, because those are the companies that carry built-in gains exposure in the first place.

Whose Job Was the Filing?

This is the part no accounting article covers, and it is the part that is actually a legal question.

Most operating and shareholder agreements do not say who is responsible for filing the company's return, or by when, or what happens if they do not. The penalty does not care about that silence. It lands on the entity and passes through to every owner, including the passive ones who never saw a draft return.

Practice pointer. Put three things in the agreement. Who files, that the extension must be filed by the original due date whether or not the return is ready, and who bears a penalty caused by a failure to do it. All three are one paragraph, and the paragraph is worth $7,050 the first time it is needed.

If you are the minority owner and the manager will not file, the fastest move is a written demand for the books and records. See what a minority owner can require.

Frequently Asked Questions

Sources of Law

• IRC §6699, failure to file an S-corporation return, per shareholder per month to a 12-month cap, with a reasonable-cause exception. §6037(a), the return requirement. §6081 and Form 7004, the six-month extension. §1374 (built-in gains) and §1375 (excess net passive income), both payable by the original due date. §6751(b)(2)(B), the exception to supervisory approval for penalties automatically calculated through electronic means. (retrieved 2026-09-01)
• Tax Court: ATL & Sons Holdings, Inc. v. Commissioner, 152 T.C. No. 8 (2019), a reported opinion holding an S corporation liable under §6699 where its shareholders extended and timely filed their own returns but no extension was filed for the company. Babak Roshdieh, M.D. Corp. v. Commissioner, 2014 T.C. Summ. Op. 113 ⚠️ (a Summary Opinion, which may not be cited as precedent under §7463(b), described here for its facts only). ⚠️ Both opinions state the penalty at the figure in force at the time; the current indexed amount is above it.

What I See in the Two Weeks Before the Deadline

In 14 years of law practice, the calls I take in early September are not from people who forgot. They are from people who believed somebody else had it handled.

A common question I hear is, "My accountant filed my extension, so we are fine, right?" That is the sentence I stop on, because your accountant may well have extended you. Whether anybody extended the company is a different filing by a different filer, and the Tax Court has already held a company liable on precisely that split.

I have come across a case that shows why the paperwork matters more than the recollection. A doctor's professional corporation insisted it had extended its return to September 15 and filed in October. The IRS transcript showed no extension had been filed at all, and showed the return arriving the following January. Disagreeing with a transcript is not the same as rebutting one, and the company lost.

Practice pointer. Get the Form 7004 acceptance in writing and keep it with the corporate records rather than in an email thread. When the argument comes, it is the transcript against your file, and a file with nothing in it does not argue back.

Avoid waiting for the return to be finished before filing anything. A return filed with a reasonable estimate stops the per-shareholder clock and can be amended. A perfect return filed in November costs $235 a month for every owner it belongs to.

One honest limit. Preparing and filing the return is your CPA's work and I do not do it. What I do is the agreement that says whose job it was, the penalty defense when reasonable cause is genuinely there, and the argument with Appeals when it is not straightforward.

Kevin D. Klagge, Esq., admitted in Florida since 2012. Any case described is a decision of a court rather than a matter handled by this firm. General information rather than advice on your situation.

Updated on September 1, 2026. Reviewed by Kevin D. Klagge, Esq., Fla. Bar No. 99502. Attorney Kevin Klagge represents families, businesses, and international clients in estate and tax planning, business structuring, and international law, with a focus on Florida legal tools. He litigates estate and business issues in court. General information about federal law, not legal or tax advice, and no attorney-client relationship is created. Filing dates and penalty amounts change; confirm the current figures with your CPA. Do not send confidential information until we have agreed to represent you.