What Is Form 1120?
Form 1120 is the US corporate income tax return. Most foreign LLC owners meet it in a surprising way — not to pay corporate tax, but as the cover sheet the IRS makes them attach to Form 5472 every year. Here's what the form is, who files it, and why a company with no activity still uses it.
What it is
Form 1120 is officially the US Corporation Income Tax Return. It's the form a US C-corporation files each year to report its income, deductions, and profit, and to calculate the federal corporate income tax it owes — a flat 21% of taxable profit (as of 2026). If a company is a normal C-corp doing business in the US, Form 1120 is where its yearly tax story is told, the corporate equivalent of the personal 1040 that individuals file.
It's worth placing it among its siblings, because the numbers look confusingly alike. Form 1120 is for C-corporations. Form 1120-S is for S-corporations, a different tax treatment. Form 1065 is for partnerships. And a single-member LLC is usually "disregarded," meaning it normally files no separate business return at all — its activity just flows onto its owner's return. That last point is what makes the foreign-owned case below feel counterintuitive.
Who files a normal 1120
A standard Form 1120 is filed by a company that has actually chosen to be taxed as a C-corporation — for example, a US startup that expects to raise venture capital, or a business that elected corporate treatment for its own reasons. That company completes the whole form: revenue, expenses, taxable income, and the tax due. For a calendar-year corporation the return is generally due by the 15th day of the fourth month after year-end (mid-April), with a six-month extension available by filing Form 7004. This is the "real" 1120 — a genuine tax return that calculates and reports corporate tax.
The pro-forma 1120: why foreign LLC owners meet this form
Here's the twist that catches non-resident owners off guard. A foreign-owned single-member LLC — the most common structure for a non-resident e-commerce seller — is normally a disregarded entity that wouldn't file its own return. But the IRS still requires it to report its dealings with its foreign owner on Form 5472, and Form 5472 cannot be filed on its own. It has to ride along with a Form 1120.
So the IRS has these companies file what's called a "pro-forma" Form 1120 — a stripped-down version used purely as an envelope. You don't fill it in as though the LLC were a corporation paying 21% tax. Instead you complete only the identifying information at the top (the company's name, address, and EIN), write "Foreign-Owned U.S. DE" across the top as the instructions direct, and attach the Form 5472 that carries the actual detail. In this arrangement the 1120 is the cover sheet and the 5472 is the real content. The company isn't paying corporate income tax through it; it's using the 1120 as the required vehicle to deliver the 5472.
Why this matters even with zero activity
The reason to care is that this filing is owed every year, even if the company did nothing. Because forming the LLC and moving any money in or out counts as a reportable transaction with the foreign owner, the pro-forma 1120 plus 5472 package is due annually from the very first year — regardless of whether the business earned a dollar. A couple of features make it easy to get wrong:
- It can't be e-filed. As of 2026, the foreign-owned disregarded-entity package goes to the IRS by mail or fax only, which makes it easy to forget or misplace.
- It depends on the EIN. You can't file it without the company's EIN, so an EIN problem quietly becomes a filing problem.
- The penalty lives on the 5472 side. Missing the package carries a penalty that starts at $25,000, explained in full in our Form 5472 penalty guide. The pro-forma 1120 itself owes no tax, but skipping the combined filing is expensive.
The practical takeaway: if you own a foreign single-member LLC, "Form 1120" almost certainly means the pro-forma cover sheet, not a corporate tax bill — but it's a filing you must make on time each year, not an optional one.
A quick word on income tax
Filing the pro-forma 1120 doesn't mean you owe US income tax. Whether you owe actual tax is a separate question, decided by whether your company is engaged in a US trade or business and by any tax treaty between the US and your country — not by the existence of this form. It's the same distinction we draw between the different US taxes: an information filing and a tax bill are not the same thing, and you can owe the filing while owing no tax.
What we handle for you
We prepare and file your Form 1120 correctly for your situation — the full corporate return if you've genuinely elected C-corp treatment, or the pro-forma 1120 with its attached Form 5472 if you own a foreign single-member LLC — on time, by the right method, every year. If prior years were missed, we handle the catch-up filings too. It's a core part of our US market-entry and e-commerce work. Tell us about your company and we'll make sure the right version of this form is filed the right way.