IRS Form 1120 (U.S. Corporation Tax Return): Guidance for Completing, Filing, and Amending

Summary

This practice note provides an overview of the advantages and disadvantages of filing as a C corporation (Form 1120) and how a C corporation reports income, gains, losses, deductions, credits, payments, and federal income tax liability on Form 1120. The practice note also outlines the client engagement process and the process a tax practitioner should follow when preparing Form 1120 for 2025 tax year returns filed during the 2026 filing season. In addition, this note provides guidance for completing, filing, and amending Form 1120, including the information that must be gathered and current filing-season considerations such as electronic filing requirements, current Form 1120 instructions, and enacted federal tax law changes affecting corporate returns, including changes under the One Big Beautiful Bill Act, Pub. L. No. 119-21.