Form 1120-F due dates depend on one fact: whether the foreign corporation keeps an office or place of business in the United States. If it does, the return is due on the 15th day of the fourth month after the tax year ends, which is April 15 for a calendar-year filer. If it does not, the deadline moves to the 15th day of the sixth month after year-end, or June 15 for a calendar-year filer.1Internal Revenue Service. Instructions for Form 1120-F A six-month extension is available on Form 7004, but missing the filing deadline without a protective return on file can permanently strip the corporation’s right to claim deductions against U.S. income.
Which Deadline Applies to You
The office-or-no-office distinction is the only variable most filers need to check. A foreign corporation with any U.S. office or place of business follows the fourth-month rule; one operating entirely from outside the country gets the extra two months.1Internal Revenue Service. Instructions for Form 1120-F
Two adjustments can shift these dates. When April 15 or June 15 lands on a Saturday, Sunday, or federal holiday, the deadline rolls to the next business day. And corporations with a fiscal year ending June 30 file on an accelerated schedule: the return is due the 15th day of the third month after year-end, which works out to September 15. A short tax year ending anywhere in June follows the same accelerated timing.2Internal Revenue Service. Instructions for Form 1120-F
These dates govern when the completed return must reach the IRS. Tax payments run on a separate track, described below.
Extending the Deadline With Form 7004
A foreign corporation that cannot file on time can get an automatic six-month extension by submitting Form 7004 on or before the original due date.3Internal Revenue Service. About Form 7004 For a calendar-year corporation with a U.S. office, filing Form 7004 by April 15 pushes the return deadline to October 15. Without a U.S. office, Form 7004 filed by June 15 extends the deadline to December 15.4Internal Revenue Service. Instructions for Form 7004
The extension only buys time to file. It does not extend the time to pay. The corporation still has to estimate its liability and remit the full amount by the original due date. Filing Form 7004 and ignoring the payment deadline produces late-payment penalties and interest on the unpaid balance from day one, regardless of how much extra time the extension allows for paperwork.
Estimated Tax Payment Dates
A foreign corporation that expects to owe $500 or more in U.S. income tax for the year must make quarterly estimated payments. The installments fall on the 15th day of the fourth, sixth, ninth, and twelfth months of the tax year, which is April 15, June 15, September 15, and December 15 for a calendar-year filer.1Internal Revenue Service. Instructions for Form 1120-F
Each installment typically covers 25% of the expected annual liability. Because the underpayment penalty is calculated on each installment period separately, catching up later does not undo a shortfall earlier in the year.5Internal Revenue Service. Underpayment of Estimated Tax by Corporations Penalty Branch profits tax is an exception to all of this: no estimated payments are required, and the branch profits liability is settled when the return itself is filed.1Internal Revenue Service. Instructions for Form 1120-F
A corporation with a U.S. office must pay through the Electronic Federal Tax Payment System (EFTPS). One without a U.S. office can use EFTPS with a U.S. bank account, arrange a same-day wire, or pay by check or money order.1Internal Revenue Service. Instructions for Form 1120-F
Penalties for Filing or Paying Late
Late filing and late payment carry separate penalties, and they can run at the same time.
- Failure to file: 5% of the unpaid tax for each month or partial month the return is late, capped at 25%. If the return is more than 60 days late, the minimum penalty is the lesser of $525 or 100% of the tax owed for returns due in 2026.6Internal Revenue Service. Failure to File Penalty7Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
- Failure to pay: 0.5% of the unpaid tax per month, also capped at 25%. That rate rises to 1% if the tax stays unpaid 10 days after the IRS issues a notice of intent to levy.7Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
When both penalties apply in the same month, the failure-to-file penalty is reduced by the failure-to-pay amount. The filing penalty maxes out after five months, but the payment penalty keeps accruing until the balance is cleared.6Internal Revenue Service. Failure to File Penalty
Interest runs alongside the penalties. The IRS resets its rate quarterly; the corporate underpayment rate is 7% for the first quarter of 2026 and 6% for the second quarter.8Internal Revenue Service. Quarterly Interest Rates Interest starts on the original due date and continues until the balance is paid, whether or not an extension was filed.
The Bigger Risk: Losing Deductions
The financial penalties above are usually not the worst part of missing the deadline. Under Section 882, a foreign corporation is allowed deductions and credits against its effectively connected income only if it files a true and accurate return.9Office of the Law Revision Counsel. 26 USC 882 – Tax on Income of Foreign Corporations Connected With United States Business The regulations tie that allowance to timely filing.10eCFR. 26 CFR 1.882-4 – Allowance of Deductions and Credits to Foreign Corporations Skip the return, and the IRS can tax the corporation on gross U.S. income with no offsets, which for a business with substantial expenses can dwarf any penalty.
Protective Returns
A foreign corporation that is uncertain whether it has ECI or a U.S. filing obligation can preserve its deduction rights by filing a protective return. The regulations generally require it within 18 months of the original due date. Once that window closes, deductions and credits are permanently lost for that year.
A protective return does not need final numbers. It is a placeholder that keeps the door open for a later amended return with actual figures. For any foreign corporation operating near the line of U.S. taxability, filing a protective return is inexpensive insurance against a much larger bill.
Treaty Positions Ride With the Return
If Form 1120-F claims a benefit under a U.S. tax treaty, each treaty-based position must be disclosed on Form 8833 attached to the return.11Internal Revenue Service. About Form 8833, Treaty-Based Return Position Disclosure Under Section 6114 or 7701(b) That includes anything from a reduced branch profits tax rate to a full exemption of certain income.12Office of the Law Revision Counsel. 26 USC 6114 – Treaty-Based Return Positions The penalty for missing the disclosure is $10,000 per failure for a C corporation, and each undisclosed position counts separately.13Office of the Law Revision Counsel. 26 USC 6712 – Failure to Disclose Treaty-Based Return Positions The form itself is short, but it is easy to overlook on a busy international return, and the deadline for filing it is the deadline for filing the return.