What Is Form 1120?
Form 1120 is the US corporate income tax return. A foreign-owned US disregarded entity may also use a pro-forma 1120 as the cover sheet for Form 5472 when that information return is required. Here is what the form is, who files it, and why a quiet year can still contain reportable transactions.
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 a quiet year can still require the package
Form 5472 applicability depends on the entity, foreign ownership, and whether there were reportable transactions. Revenue is not the test: forming the LLC, contributing capital, paying expenses for it, or moving money between owner and company can be reportable. That is why a business with no sales may still need a pro-forma Form 1120 and Form 5472. It is not accurate to say that every foreign-owned LLC files in every year regardless of the facts. Review the current IRS Form 5472 instructions for the filing tests and procedure. A couple of features make the package 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 and Form 5472 applies, “Form 1120” may mean the pro-forma cover sheet rather than a corporate tax bill. The filing is mandatory when the tests are met, but the conclusion must follow the entity and transaction facts.
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 the Form 1120 appropriate to the engagement — a full corporate return for a C-corporation, or a pro-forma 1120 with Form 5472 when the foreign-owned disregarded-entity rules apply. We also review prior years for missed required filings. This is part of our US market-entry and e-commerce work. Tell us about your company and we will identify the applicable filing before preparing it.