Sep 15

Tuesday, September 15, 2026 — the last day to file your 2025 S-Corp or Partnership return if you're on an extension.

Calendar-year S-Corporations and Partnerships were originally due back in March. If you filed Form 7004 and requested an extension, you moved your deadline to September 15, 2026, and that Tuesday is the last day to submit your 2025 return. There is no additional extension after it.

Here's the catch that trips up so many owners: these returns usually don't come with a tax bill, so it's easy to treat the deadline as flexible. It isn't. The penalty for filing late has nothing to do with how much tax you owe, and it grows fast. Below is exactly who this applies to, why the cost is real, and what to have ready.

01 — WHO IT APPLIES TO

Is this date for you?

The September 15 deadline applies to any calendar-year pass-through entity that filed a valid extension by the original March 16, 2026 due date. That's two main groups:

S-Corporations (Form 1120-S)

Corporations that elected S status file an information return and issue a Schedule K-1 to each shareholder. If you extended, it's due September 15.

Partnerships (Form 1065)

Two or more owners sharing a business file Form 1065 and issue K-1s to the partners. Same extended deadline: September 15.

Multi-member LLCs

An LLC with two or more members is taxed as a partnership by default, so it files Form 1065 and follows the same date, unless it elected corporate treatment.

Note the timing gap: your extended personal return (Form 1040) isn't due until October 15.

The business return comes first on purpose, because the K-1s it produces feed each owner's individual return. File the entity late and you hold up everyone who depends on those K-1s.

02 — THE COSTLIEST MISCONCEPTION

No tax due doesn't mean no penalty

Most business owners assume that because an S-Corp or Partnership doesn't pay federal income tax at the entity level, a late return is harmless. With individual taxes, the penalty is a percentage of what you owe, so zero owed often means zero penalty. The IRS treats these returns differently.

IMPORTANT

Form 1120-S and Form 1065 are information returns. The late-filing penalty is charged per owner, per month, and it applies even if the business had no income, ran at a loss, or owes no tax at all.

So the deadline isn't really about a payment, it's about handing the IRS the data on time and getting K-1s into your owners' hands. That's why a return with a $0 tax bill can still generate a four-figure penalty.

03 — IF YOU MISS THE DATE

What filing late costs

The failure-to-file penalty runs under IRC §6698 for partnerships and §6699 for S-Corps.

The math is the same for both, and it multiplies by the number of owners:

ITEM: APPROXIMATE COST:

Late-filing penalty $255 · up to 12 months.
(per owner, per month)

Applies even with no income YES.
(loss or zero tax)

Late or incorrect K-1s Separate penalties.

Example: a partnership with 3 partners that files 4 months late owes roughly $255 × 3 × 4 = $3,060, before any K-1 penalties.

The per-owner amount is set by the IRS and adjusts periodically for inflation.

If you did slip past a deadline, relief may be available, such as First-Time Abatement for a clean compliance history, or the small-partnership exception for certain groups of 10 or fewer partners. It's worth asking about rather than just paying the notice.

04 — BEFORE YOU FILE

What to have on hand

A pass-through return is only as clean as the books behind it. Here's the base to file a complete 1120-S or 1065:

The bottleneck is almost never the form itself, it's having the books closed and the owner details reconciled. When the bookkeeping is clean, the return and its K-1s come together in a fraction of the time.

✓ Year-end financials — a closed-out profit & loss statement and balance sheet.

✓ Owner details & ownership % — each partner or shareholder and their share.

✓ Distributions & contributions — money in and out for each owner during the year.

✓ Payroll records — especially S-Corp owner "reasonable compensation" on W-2.

✓ Loans & basis tracking — capital accounts and any owner loans to the business.

✓ Last year's return — for carryovers, elections, and consistency.

One advantage of being in Florida: the state has no personal income tax, and typical pass-throughs generally aren't subject to Florida income tax at the entity level either, so owners usually don't file a Florida return on their K-1 income. If your business operates or earns income in other states, though, those states may have their own filing requirements. Better to confirm it than to assume.

05 — QUICK TIPS

So you don't leave it to the last day

Don't wait until the 15th. E-file rejections and last-minute corrections need breathing room.
Get K-1s to your owners as early as possible, they need them to finish their 1040 by October 15.
File electronically and keep the e-file acknowledgment as your proof of a timely return.
Even if the return feels imperfect, filing complete and on time stops the per-owner clock.

AUREI · BOOKKEEPING & FINANCE

Reach September 15 with clean books and ready K-1s

At Aurei we close out your books and reconcile owner details so your 1120-S or 1065 files on time, and your partners get their K-1s without the scramble. Direct communication, clear pricing, and a team that actually responds, without the distance of a traditional firm.

Let's talk before the deadline tightens.

This article is for informational purposes and reflects general federal rules for the 2025 tax year.

It is not tax, accounting, or legal advice for your specific situation.

Deadlines, penalty amounts, and relief options may vary due to individual circumstances, disaster declarations, or other IRS provisions. Consult a professional about your particular situation.

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