Form 1120

Form 1120 is the income tax return that a U.S. corporation files every year. The IRS describes its job in one sentence: domestic corporations use it to "report their income, gains, losses, deductions, credits" and to "figure their income tax liability."

Most founders arrive at this page for one of two reasons. Either they incorporated a C corporation, usually in Delaware, and they now need to know the deadline. Or they own an LLC and they are not sure whether this form applies to them at all.

The second question is the one that causes real damage, so we will answer it first. Form 1120 follows the company, not the owner. It applies because your company is treated as a corporation for federal tax, and it does not apply because you happen to be American or not American. A Delaware corporation owned 100% by a founder in Seoul files the same Form 1120, on the same date, as a Delaware corporation owned by a founder in San Francisco.

What the rule actually says

Who files it. Domestic corporations file Form 1120. "Domestic" here means the company was formed under the law of a U.S. state, not that its owners live in the United States.

An LLC is where people get lost, because an LLC is not automatically a corporation. The IRS sets the default this way:

• An LLC with one member is "treated as an entity disregarded as separate from its owner," unless it files Form 8832 and elects to be treated as a corporation.
• An LLC with at least two members is "classified as a partnership for federal income tax purposes," unless it files Form 8832 and elects to be treated as a corporation.

So a normal single-member LLC does not file Form 1120. A normal multi-member LLC does not file Form 1120 either; it files a partnership return. Your LLC only enters the Form 1120 world if you actively filed Form 8832 and chose corporate treatment. If you never filed that form, you never made that choice.

When it is due. The return is due on the 15th day of the 4th month after the end of your tax year. If your tax year is the calendar year, which is normal for a new company, your year ends on 31 December and the return is due on 15 April.

The 30 June exception is expiring, and most sources have not caught up. For years, a corporation whose tax year ended on 30 June filed on the 15th day of the 3rd month rather than the 4th, which meant 15 September. Congress ended that. Under section 2006(a)(3) of Public Law 114-41, the ordinary 4-month rule applies to a June year-end corporation for tax years beginning after 31 December 2025.

What that means in practice:

• A tax year that ran 1 July 2025 to 30 June 2026 began before the cutoff, so the old rule still applies. It is due 15 September 2026.
• A tax year beginning on or after 1 January 2026, including 1 July 2026 to 30 June 2027, follows the ordinary rule. It is due 15 October 2027.

So if you are choosing a June year end now, your deadline is 15 October, not 15 September. Articles written before this year, and the IRS instructions for tax year 2025, still state the September rule, because it was correct for the years they covered.

Here is the arithmetic for three cases:

• Year ends 31 December. Count 4 months: January, February, March, April. Due 15 April.
• Year ends 31 March. Count 4 months: April, May, June, July. Due 15 July.
• Year ends 30 June, for a tax year beginning on or after 1 January 2026. Count 4 months: July, August, September, October. Due 15 October.

Paying during the year. The annual return is not the only deadline. A corporation that expects its tax, after subtracting credits, to be $500 or more has to pay estimated tax in installments during the year. The installments are due on the 15th day of the 4th, 6th, 9th and 12th months of the tax year. For a calendar-year company that means 15 April, 15 June, 15 September and 15 December.

Two details matter here. The threshold is $500, which is low enough that most profitable companies cross it in their first good year. And the payments have to be made electronically. You cannot mail a cheque for these.

🇺🇸 If the IRS counts you as a U.S. person

If your company is a corporation, you file Form 1120 by the deadline above and you pay estimated tax during the year once you expect to owe $500 or more.

There is one choice open to you that is not open to everyone. A U.S. corporation can elect to be taxed as an S corporation, which files Form 1120-S instead of Form 1120 and passes its income through to the shareholders. Whether that is a good idea depends on your situation, and it is a separate page in this guide.

The relevant point on this page is that the S election is a real fork in the road. Take it, and you stop filing Form 1120. Do not take it, and Form 1120 is your return every year, including years when the company earned nothing.

🌏 If it does not

Everything in the section above about Form 1120 applies to you in exactly the same way. Same form, same deadline, same $500 estimated tax threshold, same requirement to file in years with no profit. The IRS asks about the company's residence, not yours.

One door is closed to you, and it is closed by statute rather than by policy. Under 26 U.S.C. § 1361(b)(1)(C), a corporation cannot be an S corporation if it has a shareholder who is a nonresident alien. So the escape route from Form 1120 into Form 1120-S is unavailable while a nonresident alien holds shares.

Read that rule carefully, because it turns on tax residence and not on nationality. A resident alien, meaning a foreign citizen the IRS treats as a U.S. resident under the green card test or the substantial presence test, can be an S corporation shareholder. A nonresident alien cannot. If you are not sure which one you are, run the two tests on the U.S. person page in this guide before you assume anything.

There is a second thing you should not confuse with this form. If you own a single-member LLC and you never elected corporate treatment, you do not file Form 1120 as an income tax return. But a foreign-owned disregarded LLC does have to file Form 5472 together with a pro forma Form 1120, which is an information filing, not a tax return. It uses the same form number and it is a different obligation. We cover it on its own page.

Where the two lanes actually stand

This is one of the pages in the guide where the two lanes do not split. The table below shows what stays the same, and marks the one row where residency changes the answer.

Only the last row differs, and even that row is not about the form itself. It is about whether you are allowed to leave Form 1120 for a different return.

Common mistakes

🇺🇸 If the IRS counts you as a U.S. person

• Reading an older article about the 30 June fiscal year end and assuming the deadline is still 15 September. For tax years beginning after 31 December 2025 it is 15 October, like every other fiscal year end.
• Skipping the return in a year with no revenue. A corporation files whether or not it earned anything. The obligation comes from being a corporation, not from making money.
• Waiting until the annual return to pay anything, after expecting more than $500 of tax. The estimated tax instalments were due during the year.

🌏 If it does not

• Assuming that a company with no U.S. owners somehow files a different corporate return. It does not. The corporation is domestic, so it files Form 1120.
• Assuming an S election is available and only discovering later that it was never legal. Section 1361(b)(1)(C) blocks a nonresident alien shareholder, and an invalid election creates a mess to unwind.
• Mixing up the pro forma 1120 filed with Form 5472 by a foreign-owned disregarded LLC with a real Form 1120 income tax return. They are two different obligations that share a number.
• Assuming your single-member LLC is a corporation because you were told "you have a company in the U.S." It is disregarded by default until you file Form 8832.

FAQ

Does my LLC file Form 1120?

Only if it elected to be taxed as a corporation by filing Form 8832. By default, a single-member LLC is disregarded and a multi-member LLC is a partnership. Neither default files Form 1120 as an income tax return. One thing to note if you are a foreign owner: a foreign-owned single-member LLC still files a pro forma Form 1120 as a cover sheet for Form 5472. That is an information filing, not the return described on this page.

I own a U.S. corporation but I live abroad. Do I still file Form 1120?

Yes. The form belongs to the company, and the company was formed under the law of a U.S. state. Your own residency does not change the corporation's return, its deadline, or its estimated tax rules.

When exactly is Form 1120 due?

On the 15th day of the 4th month after your tax year ends. A calendar-year corporation files on 15 April. There used to be an exception for a tax year ending on 30 June, which moved the date to the 15th day of the 3rd month, but that exception applies only to tax years beginning before 1 January 2026. A June year end starting after that date follows the ordinary 4-month rule, so the last year under the old rule is 1 July 2025 to 30 June 2026, due 15 September 2026.

Do I have to file if my corporation had no income?

Yes. Form 1120 is the return for a domestic corporation, and a year with no revenue is still a tax year. Not filing does not save you anything and it creates a gap in the company's record.

What is the $500 rule?

If your corporation expects to owe $500 or more in tax after credits, it must pay estimated tax during the year, in four instalments, on the 15th day of the 4th, 6th, 9th and 12th months of the tax year. The payments must be made electronically.

Can I choose S corporation status to avoid Form 1120?

Only if every shareholder qualifies. Under 26 U.S.C. § 1361(b)(1)(C), a corporation with a nonresident alien shareholder cannot be an S corporation. Note that this depends on tax residence, not on citizenship. A foreign citizen who is a resident alien for tax purposes can be a shareholder.

Is the pro forma 1120 that goes with Form 5472 the same thing as this form?

No. A foreign-owned single-member LLC that is disregarded for tax files Form 5472 together with a pro forma Form 1120. That is an information filing. It is not the corporate income tax return described on this page, and it does not mean your LLC is a corporation.

What is the corporate tax rate on Form 1120?

We do not quote a rate on this page. Rates and thresholds change, and a number copied from an article is the wrong place to get one. Check the current instructions for Form 1120 on the IRS site, which are linked below.