What is Form 1120?
Form 1120, officially called the "U.S. Corporation Income Tax Return," is the primary tax document that C corporations must file with the Internal Revenue Service (IRS) to report their income, deductions, and tax liability for the tax year.
Who Must File Form 1120?
Required filers include:
C corporations (domestic corporations)
Foreign corporations engaged in trade or business in the United States
Corporations with gross receipts or total assets of $250,000 or more
Exceptions:
S corporations file Form 1120S instead
LLCs typically don't file Form 1120 (unless they elect corporate taxation)
Partnerships file Form 1065
Key Filing Requirements and Deadlines
Standard Filing Deadline
Due Date: The 15th day of the 4th month after the corporation's tax year ends
For calendar year corporations: April 15th
For fiscal year corporations: 15th day of the 4th month after fiscal year-end
Extension Options
Automatic 6-month extension available by filing Form 7004
Extension deadline: October 15th (for calendar year corporations)
Important: Extensions are for filing only, not for payment of taxes owed
Essential Components of Form 1120
Income Reporting
Gross receipts or sales (Line 1a)
Cost of goods sold (Line 2)
Gross profit (Line 3)
Dividends and interest income
Capital gains and losses
Other income sources
Deductions
Salaries and wages
Repairs and maintenance
Bad debts
Rent expenses
Taxes and licenses
Interest expense
Charitable contributions (limited to 10% of taxable income)
Depreciation
Other allowable business deductions
Tax Calculation
Current Corporate Tax Rate: 21% flat rate (as of 2025)
Alternative Minimum Tax (AMT) considerations
Tax credits that may apply
Estimated tax payments made during the year
Supporting Schedules and Forms
Commonly Required Schedules
Schedule C: Dividends and Special Deductions
Schedule J: Tax Computation and Payment
Schedule K: Other Information
Schedule L: Balance Sheet
Schedule M-1: Reconciliation of Income per Books with Income per Return
Schedule M-2: Analysis of Unappropriated Retained Earnings
Additional Forms That May Be Required
Form 4562: Depreciation and Amortization
Form 8825: Rental Real Estate Income and Expenses
Form 8949: Sales and Other Dispositions of Capital Assets
Schedule D: Capital Gains and Losses
Federal Tax Payment Requirements
Estimated Tax Payments
Corporations must make quarterly estimated tax payments if they expect to owe $500 or more in tax for the current year.
Due Dates for Estimated Payments:
1st Quarter: April 15th
2nd Quarter: June 15th
3rd Quarter: September 15th
4th Quarter: December 15th
Payment Methods
Electronic Federal Tax Payment System (EFTPS)
Online banking
Phone payments
Wire transfers
Check or money order (with proper vouchers)
Common Mistakes to Avoid
Filing Errors
Missing the filing deadline without requesting an extension
Incorrect calculation of taxable income
Failing to reconcile book income with tax income
Incomplete supporting schedules
Record Keeping Issues
Inadequate documentation for deductions
Missing receipts for business expenses
Poor organization of financial records
Failure to maintain depreciation schedules
Penalties and Consequences
Late Filing Penalties
5% of unpaid tax for each month (or part of month) the return is late
Maximum penalty: 25% of unpaid tax
Minimum penalty: $435 (for returns over 60 days late)
Late Payment Penalties
0.5% of unpaid tax for each month (or part of month) after due date
Maximum penalty: 25% of unpaid tax
Interest Charges
Applied to both unpaid taxes and penalties
Rate is determined quarterly by the IRS
State Tax Considerations
Remember that federal filing is just one part of your tax obligations:
Most states require separate corporate income tax returns
State filing deadlines may differ from federal deadlines
State tax rates and rules vary significantly
Some states have no corporate income tax
Multi-state businesses may have complex apportionment requirements
Getting Professional Help
Given the complexity of corporate taxation, consider professional assistance when:
Your corporation has significant revenue or complex transactions
You're dealing with multi-state operations
You have questions about specific deductions or credits
You've received notices from the IRS
You're behind on filing requirements
Conclusion
Form 1120 and federal corporate tax compliance require careful attention to detail and thorough understanding of tax laws. Proper preparation, timely filing, and accurate record-keeping are essential for avoiding penalties and maintaining good standing with the IRS.
For personalized assistance with your corporation's tax filing requirements, consult with a qualified tax professional who can guide you through the specific requirements that apply to your business situation.
This article provides general information about US federal taxation and Form 1120. Tax laws are complex and change frequently. Always consult with a qualified tax professional for advice specific to your situation.