Form detail
IRS Form 1120
U.S. Corporation Income Tax Return
Country
United States
Revision year
2024
Methods
paper, efile
Updated
2026-05-20
U.S. Corporation Income Tax Return
Annual income tax return for C corporations.
Who must file: Domestic corporations subject to U.S. federal income tax at the entity level, including most C corporations.
Practical overview
Form 1120 reports taxable income at the entity level at the flat 21 percent federal rate (Tax Cuts and Jobs Act). Common issues include book-tax reconciliation on Schedule M-1 or M-3, dividends-received deduction calculations, NOL carryforward limitations under 382, and state-level pass-through entity tax interaction. C-corp returns are due April 15 (calendar year), not March 15.
Practical steps
- Complete book-tax reconciliation on Schedule M-1 or M-3.
- Confirm the corporation is not a personal holding company, accumulated earnings, or other special-rule corporation.
- Compute tax at 21 percent and reconcile estimated tax payments.
- Attach K-2/K-3 international schedules for relevant items.
- File by April 15 for calendar-year corporations with extension via Form 7004.
Due-date notes
April 15 for calendar-year corporations (15th day of the 4th month after year-end for fiscal-year filers).
Timing: April 15
Extension reference: Form 7004
Penalty snapshot
Late-filing penalty generally 5 percent per month up to 25 percent; underpayment penalty applies under Section 6655.
Related forms
Related guides
Related citations
Computed from the cross-reference graph. Links open the related entity on this site.
Primary sources
- About Form 1120Verified 2026-05-20
- Instructions for Form 1120Verified 2026-05-20
Important disclaimer
This library is for general tax education only. Always verify filing obligations, due dates, and tax consequences against the cited primary source or with a qualified tax professional.