Form 1120-A, the short-form U.S. corporation income tax return, is obsolete. The IRS has not accepted it for any tax year beginning after 2006, and there is no current short-form equivalent. Every domestic C corporation now files the standard Form 1120, regardless of how small its receipts or assets are.
What Form 1120-A Used To Be
Form 1120-A was a streamlined corporate return with three parts: a taxable-income calculation, the tax computation, and a simplified year-end balance sheet. It existed so that small corporations could avoid the full Form 1120 schedules.
Qualifying was strict. A corporation had to meet every one of the following:
- Gross receipts under $500,000 for the tax year.
- Total assets under $500,000 at year-end.
- No membership in a controlled group of corporations.
- No foreign shareholders and no ownership in a foreign entity.
- Not in the middle of a plan of liquidation or dissolution.
- Not a personal holding company, and not filing a consolidated return.
Tripping any one of those conditions pushed the corporation onto Form 1120. Once the IRS retired the short form, the distinction stopped mattering: all C corporations file Form 1120.
What You File Instead
Form 1120 is now the only corporate income tax return the IRS accepts from C corporations. It covers income, deductions, tax computation, credits, and payments in a single document. The federal corporate tax rate is a flat 21% applied to taxable income after allowable deductions.
Deadline and Extension
Form 1120 is due on the 15th day of the fourth month after the end of the corporation’s tax year, which is April 15 for a calendar-year filer.1Internal Revenue Service. Publication 509, Tax Calendars Filing Form 7004 grants an automatic six-month extension, moving the deadline to October 15 for calendar-year corporations.2Internal Revenue Service. About Form 7004, Application for Automatic Extension of Time to File Certain Business Income Tax, Information, and Other Returns The extension covers filing only. Any tax owed is still due by the original date, and interest accrues on unpaid balances from that day forward.
Note the deadline shift if you are comparing to older filings. The original Form 1120-A deadline was the 15th day of the third month, which was March 15 for calendar-year corporations. That earlier date applied only to returns for tax years ending in 2006 or before.
E-Filing Rules
Electronic filing is not always mandatory, but the threshold that triggers mandatory e-filing has come down sharply. Final regulations issued in 2023 lowered the general e-file threshold from 250 returns to 10, calculated by aggregating all information returns a corporation files.3Internal Revenue Service. Form 1120/1120-F/1120-H/1120-l/1120-PC/1120-REIT/1120-RIC E-File If your corporation files 10 or more information returns in total (W-2s and 1099s combined, for example), you likely need to e-file the income tax return as well.
Fixing an Old Form 1120-A Return
If you need to correct a return that was originally filed on Form 1120-A, the IRS still accepts Form 1120-X, Amended U.S. Corporation Income Tax Return, for that purpose. The instructions for Form 1120-X specifically list correcting a Form 1120 or Form 1120-A as one of its uses.4Internal Revenue Service. About Form 1120-X, Amended U.S. Corporation Income Tax Return
Time limits usually close the door. Form 1120-X generally must be filed within three years after the date the original return was filed, or within two years after the corporation paid the tax, whichever is later. A return filed before its due date counts as filed on the due date for this calculation. Longer windows apply for net operating loss carrybacks (three years after the due date of the loss year’s return, including extensions) and for bad debts or worthless securities (seven years after the due date of the return for the year they became worthless).5Internal Revenue Service. Instructions for Form 1120-X
Because Form 1120-A was last valid for tax years ending in or before 2006, the standard three-year window for amending those returns closed long ago. The extended deadlines for carrybacks or worthless debts could theoretically reach further, but at this distance they almost never do. For practical purposes, old Form 1120-A returns are final. On the same timing logic, the IRS assessment window for those years has also closed under normal rules, though a return that was never filed has no time limit.6Internal Revenue Service. Time IRS Can Assess Tax
Late Filing Costs on Current Returns
If you are filing Form 1120 late rather than reviewing an old return, the penalty structure matters. The failure-to-file penalty is 5% of the unpaid tax for each month or partial month the return is late, up to a maximum of 25%.7Internal Revenue Service. Failure to File Penalty For returns required to be filed in 2026, if the return is more than 60 days late, the minimum penalty is the lesser of $525 or 100% of the tax owed.8Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
Interest runs on top of that. The corporate underpayment rate is 7% for the first quarter of 2026 and 6% for the second quarter, with an extra two percentage points added on large corporate underpayments (generally over $100,000). The interest compounds daily.9Internal Revenue Service. Quarterly Interest Rates
The Closest Thing to a Short Form Today
Small corporations that liked Form 1120-A because it was less paperwork often do better with S corporation status than with C corporation status. An S corporation passes income and losses through to shareholders’ personal returns and avoids corporate-level tax. It files Form 1120-S rather than Form 1120.
To qualify, the corporation must meet all of the following:10Internal Revenue Service. S Corporations
- Be a domestic corporation.
- Have 100 or fewer shareholders. Family members can often be counted as a single shareholder.
- Have only eligible shareholders: individuals, certain trusts, and estates. Partnerships and other corporations cannot hold shares.
- Have no nonresident alien shareholders. Every shareholder must be a U.S. citizen or resident.
- Issue only one class of stock, though voting rights within that class can differ.
- Not be an ineligible type, such as certain financial institutions, insurance companies, or domestic international sales corporations.
The election is made by filing Form 2553, Election by a Small Business Corporation.11Internal Revenue Service. About Form 2553, Election by a Small Business Corporation To take effect in the current tax year, Form 2553 generally must be filed by the 15th day of the third month of that year. A late-filed election may still apply for the following year. If your corporation is small, closely held, and modestly profitable, running the S election past a tax professional is often worth the hour.