Form 1120: U.S. Corporation Income Tax Return

Form 1120 is the federal income tax return of a domestic corporation, used to report its income, gains, losses, deductions and credits and to figure its tax. Unless a corporation is exempt under section 501, it has to file whether or not it has taxable income, so a newly formed Delaware corporation with no revenue still owes a Form 1120 for its first year.

Two kinds of entity file the full version. One is an ordinary corporation under state law that has not made an S election. The other is a domestic LLC that filed Form 8832 to be classified as an association taxable as a corporation; it attaches a copy of the Form 8832 to the return for the year the election took effect. A third group files a pro forma version, covered below.

Some corporations file a different return: Form 1120-S for an S corporation, Form 1120-F for a foreign corporation, Form 990-T for an exempt organization with unrelated business income. An LLC with several owners is generally a partnership that files Form 1065, and a single-member LLC is generally disregarded, unless either one elected corporate treatment.

It depends on whether the corporation made an S election that the IRS accepted. Without one it files Form 1120 and pays tax itself. With one it files Form 1120-S, and the income passes through to shareholders on Schedule K-1.

Foreign ownership is the usual reason founders land on the left-hand column: the Form 2553 instructions say an S corporation can have no nonresident alien shareholders. The returns are not interchangeable year to year, either. The same instructions say not to file Form 1120-S for any year before the election takes effect, and to keep filing Form 1120 until it does.

See Form 2553 for the election and the Form 1120-S page for the S return. The trade-offs are in our guide to LLC vs S corporation taxes.

A corporation files by the 15th day of the 4th month after its tax year ends. For a calendar-year corporation that is April 15, or the next business day when the date lands on a weekend or legal holiday. A new corporation's first return covers a short year, counted from that year's end.

A corporation with a June 30 year end had its own rule for a tax year that began before January 1, 2026: it files by the 15th day of the 3rd month (September 15, 2026 for a year ended June 30, 2026), and Form 7004 gives it 7 months. For tax years beginning in 2026, the Form 7004 instructions give the usual 6 months.

What Form 7004 does. File it by the regular due date; it can be e-filed, and the IRS contacts you only if it disallows the request. The extension covers filing, not payment, and interest runs from the regular due date. One relief applies: a corporation with an extension isn't charged the late-payment penalty if the tax it estimated on the form, or paid by the regular due date, is at least 90% of the final tax and the balance is paid by the extended due date.

Estimated tax has its own calendar. A corporation expecting $500 or more of tax pays installments on the 15th day of the 4th, 6th, 9th and 12th months of its year, by electronic funds transfer; the last 2026 installment is Tuesday, December 15, 2026. Delaware's annual report runs on a separate March 1 date, covered in our Delaware C corporation compliance guide.

The tax is the corporation's own: the instructions have it multiply taxable income by 21%, and the IRS page on forming a corporation says the corporation does not get a tax deduction when it distributes dividends to shareholders. That is the second layer people mean when they compare a C corporation with an S corporation. The corporation pays tax on the profit, and what it later distributes is reported to shareholders on Form 1099-DIV.

A few parts of the return catch first-time filers:

• Balance sheet and reconciliations. Schedule L reports balance sheets per books, and Schedule M-1 reconciles book income with income per the return. A corporation with total receipts and total assets under $250,000 can skip Schedules L, M-1 and M-2 by checking Yes on Schedule K, question 13. At $10 million or more of total assets, Schedule M-3 replaces Schedule M-1.
• Ownership questions on Schedule K. Question 4 leads to Schedule G for owners holding 20% or more directly, or 50% or more of the voting power directly or indirectly. Question 7 asks whether one foreign person owned at least 25% of the voting power or value, with the percentage on line 7a and the owner's country on line 7b.
• The address. The instructions say not to use the registered agent's address. A Delaware corporation run from another state enters its principal office or place of business.

Two situations get mixed up, and the IRS treats them differently.

A foreign-owned Delaware C corporation files the full Form 1120. It is a domestic corporation, so the rule that every domestic corporation files applies, income or not. If it is 25% foreign-owned and had a reportable transaction with a related party during the year, it also attaches Form 5472. Failing to file Form 5472 or keep the required records carries a $25,000 penalty per reporting corporation.

A foreign-owned single-member LLC files only a pro forma Form 1120, as the cover for Form 5472, in years with a reportable transaction. The LLC is disregarded for income tax, but for the 25% foreign-owned rules the IRS treats it as a separate domestic corporation. The pro forma return needs only the entity's name and address and items B and E, with "Foreign-owned U.S. DE" written across the top. It can't be e-filed; it goes by fax or mail to a dedicated IRS number and address, and so does a Form 7004 for it. The deadline, fax number and penalty mechanics are in our Form 5472 guide for foreign-owned LLCs.

Electing corporate status swaps the second case for the first. If that LLC files Form 8832 to be taxed as a corporation, the pro forma version stops and a full Form 1120 starts; see the Form 8832 page. Electing S status instead is not open to an entity with a nonresident alien owner.

The instructions set out these charges, and interest runs on top of them, even when an extension was granted.

• Late filing: 5% of the unpaid tax for each month or part of a month the return is late, up to 25% of the unpaid tax.
• Minimum for a very late return: for a return more than 60 days late, the smaller of the tax due or $535 when the return is required to be filed in 2027, or $525 for 2026 (Revenue Procedure 2025-32 sets the 2027 amount).
• Late payment: one-half of 1% of the unpaid tax for each month or part of a month, up to 25%.

Reasonable cause is a defense. If a penalty notice arrives, send an explanation then; the instructions say not to attach one to the return.

Illustrative late-filing penalty on $20,000 of unpaid tax. Made-up figures, to the 25% cap. If the tax is also unpaid, the 0.5% late-payment charge comes out of each month's 5%, so the two together stay at $1,000 a month here.

The minimum bites at the other end. With $300 of tax due and the return 70 days late, 3 months at 5% is $45, but the minimum is the smaller of $300 and $535, so the penalty is $300.

An officer signs and dates the return: the president, vice president, treasurer, assistant treasurer, chief accounting officer, or another corporate officer, such as a tax officer, authorized to sign. A receiver, trustee or assignee who files for the corporation signs instead.

A paid preparer signs too. Anyone paid to prepare the return generally completes the Paid Preparer Use Only section, with a Preparer Tax Identification Number, and gives the taxpayer a copy; if an employee completes the form, that section stays blank. A box in the signature area lets the corporation authorize the IRS to discuss the return with the preparer who signed, which does not let the preparer receive a refund check, bind the corporation or represent it before the IRS.

How it is filed. For returns filed on or after January 1, 2024, a corporation must e-file Form 1120 if it files 10 or more returns of any type in the calendar year, counting income tax, employment tax, excise tax and information returns together. A hardship waiver can be requested in writing to the Ogden Submission Processing Center. Paper returns go to Kansas City, MO or Ogden, UT depending on the principal office's state and on whether total assets are under $10 million, with a separate Ogden P.O. box for a corporation located in a foreign country or U.S. territory.

Finbryn's role on a C corporation return is preparation support. We prepare the workpapers behind Form 1120 from your reconciled books: the trial balance tie-out, the book-to-tax adjustment schedule, support for the balance sheet and reconciliation schedules, and the ownership answers the credentialed preparer needs for Schedule K. Where Form 5472 applies, we build the related-party transaction listing that goes with it.

The workpapers and a summary go to a credentialed preparer, who reviews them, signs as the paid preparer and files the return after your authorized officer signs. Finbryn does not sign or file it. Anything that needs representation before the IRS goes to an Enrolled Agent or CPA you authorize. The C corporation tax preparation page describes the service, and the Form 5472 service page covers the foreign-owned case.

These come up repeatedly on corporate returns.

• Skipping a zero-revenue year. A domestic corporation files whether or not it had income, and the missing return is what draws the penalty.
• Treating Form 7004 as payment. It extends the filing only, and interest runs from April 15.
• Filing the wrong form around an S election. Form 1120-S before the election takes effect, or Form 1120 after it, produces notices.
• Missing Form 5472 on a 25% foreign-owned corporation. The instructions set a $25,000 penalty on the reporting corporation, and more if the failure continues 90 days after an IRS notice.
• Missing the 10-return e-file line. Payroll and information returns count toward the 10, so a small company can cross it unnoticed.