The September 15 Deadline for Foreign-Owned Multi-Member LLCs: The Extended Form 1065 Cutoff — and the Penalty That Runs Per Partner, Per Month

If your U.S. LLC has two or more owners and at least one of them is not a U.S. person, September 15 is a date you cannot ignore. For calendar-year partnerships that requested an extension back in March, September 15, 2026 is the final deadline to file Form 1065 — and the penalty for missing it is charged per partner, for every month you are late, whether or not the business made a single dollar.

Here is how the rules actually work, based on IRS guidance, so you can see where the real risks are.

Why a Multi-Member LLC Files Form 1065

By default, the IRS treats a U.S. LLC with two or more members as a partnership. A partnership does not pay federal income tax itself; instead it files an information return — Form 1065, U.S. Return of Partnership Income — that reports the business's income and expenses and shows how profits and losses are split between the owners.

This is a key difference from the single-member LLC that many non-residents start with. A foreign-owned single-member LLC is a "disregarded entity" and files Form 5472 attached to a pro forma Form 1120. The moment you add a second owner, that regime no longer applies: you are a partnership, and Form 1065 — with a Schedule K-1 for each partner — becomes your annual filing.

The Two Dates: March 15 and the September Extension

A calendar-year partnership's Form 1065 is due on the 15th day of the third month after the tax year ends — March 15. Partnerships that are not ready by then can file Form 7004 for an automatic six-month extension, which moves the deadline to September 15.

If you filed that extension in the spring, September 15, 2026 is now your hard deadline. There is no further extension. And an extension of time to file was never an extension of time to pay anything owed — including any partnership withholding tax, which we cover below.

The Penalty Non-Residents Underestimate

The Form 1065 late-filing penalty catches people off guard because it is not a flat fee and it is not tied to how much money you made. Under Internal Revenue Code section 6698, the penalty is charged per partner, per month (or part of a month) the return is late, for up to 12 months.

For 2025 tax-year returns — the ones due in 2026 — that rate is $255 per partner, per month (Revenue Procedure 2024-40). A two-owner LLC that files five months late is looking at $255 x 2 x 5 = $2,550, even with zero revenue. A three-owner LLC that forgets for a full year faces $255 x 3 x 12 = $9,180. Because the charge multiplies by both partners and months, it grows quickly and quietly.

Every Partner Needs a Schedule K-1

Form 1065 itself reports the partnership's totals, but the numbers that matter to each owner live on Schedule K-1. The K-1 shows a partner's share of income, deductions and credits, and each partner needs theirs to complete their own return. Foreign partners must receive a Schedule K-1 — and, where the rules below apply, a Form 8805.

When You Also Have to Withhold: Forms 8804 and 8805

Here is the part that separates a simple filing from an expensive one. If your LLC earns income that is effectively connected with a U.S. trade or business (ECI) and any of that income is allocable to a foreign partner, the partnership itself must withhold tax under section 1446 of the tax code.

The IRS sets that withholding at the top individual rate — currently 37% — for non-corporate foreign partners, and 21% for corporate foreign partners, applied to the foreign partner's share of effectively connected taxable income. The partnership reports it on Form 8804, issues a Form 8805 to each foreign partner, and pays the tax using Form 8813. Crucially, a Form 8805 must go to each foreign partner even if no tax ends up being withheld.

This is a partnership-level obligation. If the withholding is required and the partnership does not pay it, the partnership — not just the partner — can be liable for the tax, penalties and interest.

"But We Had No U.S. Income"

A common and costly assumption is that a partnership with no U.S.-connected profit has nothing to file. That is wrong on the return and right only on the tax. If your LLC has no income effectively connected to a U.S. trade or business, section 1446 withholding generally does not apply — but the Form 1065 information return is still due, and the per-partner late penalty still runs if you miss it. The filing obligation does not depend on whether you made money.

A Word on Penalty Relief

The IRS can abate the section 6698 penalty where there is reasonable cause, and long-standing guidance offers relief to certain small partnerships of ten or fewer partners that meet strict conditions. That relief is not automatic and the conditions do not fit every partnership — particularly those with foreign partners — so it is far safer to file on time than to rely on getting a penalty removed afterwards.

Have Questions About Your Own Situation?

Every ownership setup is a little different, and the line between "just file the 1065" and "withhold under section 1446" is exactly where non-resident owners tend to get caught. If you want to talk your own structure through with the MP Partner experts team — no pressure, no hard sell, just clear answers — we are happy to help.

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