Form 1120

Form 1120 is the annual federal income tax return filed by C corporations. It reports gross income, deductions, taxable income, and the resulting tax liability at the flat 21 percent corporate rate established by the Tax Cuts and Jobs Act, along with credits, prior payments, and any balance due or overpayment.

The return is due by the fifteenth day of the fourth month following the close of the tax year — April 15 for a calendar-year corporation — with a six-month extension available on Form 7004. Corporations with a June 30 year end follow a modified schedule. Extensions extend the filing deadline only; tax must still be paid by the original due date to avoid interest and failure-to-pay penalties.

The core return is short, but the schedules carry the substance. Schedule C reports the dividends received deduction. Schedule J computes the tax and applies credits. Schedule K captures elections and disclosures. Schedules L, M-1, and M-2 present the balance sheet, the book-to-tax income reconciliation, and the retained earnings analysis. Corporations meeting the asset threshold file the far more detailed Schedule M-3 instead of M-1. Attached forms commonly include Form 4562 for depreciation, Form 1125-A for cost of goods sold, Form 8990 for the business interest limitation, Form 6765 for the research credit, and Forms 5471 or 5472 for foreign ownership and controlled foreign corporations.

Because C corporation income is taxed at the entity level and again on distribution to shareholders, structuring decisions around reasonable compensation, dividend timing, and entity classification carry real economic weight. For CPA firms, Form 1120 preparation is inseparable from provision work under ASC 740, since the return ultimately trues up the estimated provision recorded in the financial statements.