Form 1120: the US C corporation income tax return

A C corporation is a separate taxpayer in its own right, and Form 1120 is how it reports its income and works out the tax it owes. Unlike a partnership or S corporation, whose returns mostly pass figures through to the owners, a C corporation calculates and pays tax on its own profit. This guide explains what the return does, the tax that attaches to it, when it is due, and the schedules that make it up.

What Form 1120 is

Form 1120, the U.S. Corporation Income Tax Return, is the annual federal return of a C corporation. It reports the corporation's gross income, deductions, and resulting taxable income, and computes the federal income tax on that income. The corporation files it every year it exists — including years with no income and years with a loss — until a final return is filed for the year it winds up. An LLC that has elected to be taxed as a corporation files Form 1120 as well, because for tax purposes it is treated as one.

The 21% rate and double taxation

A C corporation's taxable income is taxed at a flat 21% federal rate. The distinctive feature of the C corporation is what happens next: when the corporation distributes its after-tax profit to shareholders as dividends, those dividends are taxed again on the shareholders' own returns. This is the well-known double taxation of the C corporation, and it is worth being precise about when it applies:

• Profit that is retained and reinvested in the business is taxed once, at the corporate level.
• Profit distributed as dividends is taxed a second time in the shareholders' hands.

So a corporation that ploughs earnings back into growth is not bearing two layers on those earnings until it distributes them. The trade-off against pass-through treatment is set out in Form 1120 versus 1120-S and LLC versus C corporation.

Deadline and extension

For a calendar-year corporation, Form 1120 is due by April 15 — the 15th day of the fourth month after the tax year ends. A fiscal-year corporation applies the same rule to its own year-end. A corporation that needs more time files Form 7004 for an automatic six-month extension, moving a calendar-year deadline to October 15. That extension buys time to file, not time to pay: the tax is still due on the original date, and a corporation generally pays its tax in quarterly estimated instalments across the year rather than in a single payment at filing.

What the return reports

Form 1120 is more than a single page of numbers; it carries a set of schedules that together reconcile the corporation's books to its tax position. The main ones include a schedule for dividend income and the related deductions, the tax-computation schedule, a schedule of other information about the corporation, the balance sheet drawn from the books, and reconciliations between book income and taxable income and of retained earnings. The corporation reports its revenue, its deductible business expenses, depreciation, and any net operating loss it is carrying, and arrives at taxable income and the tax due. A year in which deductions exceed income produces a loss the corporation can carry forward under the net operating loss rules.

State returns sit alongside

The federal Form 1120 is only part of the picture. Most states impose their own corporate income tax return and, separately, a franchise tax or annual report that runs on its own clock regardless of profit — a point developed in franchise tax and annual reports. A corporation operating in more than one state can face filing obligations in each, apportioning its income between them. The federal return does not settle any of that, so the corporate compliance calendar is wider than Form 1120 alone.

Sources

This guide is written against the official and clearly labelled professional references below. Rates, thresholds and portal procedures change between reviews, so open the primary source before relying on a figure.

• About Form 1120, U.S. Corporation Income Tax Return (IRS)
• Corporations (IRS)
• Businesses (Internal Revenue Service)

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