Tax
Form 1120 (C-Corp Return)
The annual federal income tax return filed by C-corporations to report the entity's own income, deductions, and tax due — the corp pays tax at 21%.
A C-corporation is a separate taxpayer. Unlike an S-corp or partnership, income does not pass through to owners — the entity itself pays federal income tax at a flat 21% on its taxable income. Owners are taxed a second time when profit is distributed as a dividend. That is the classic 'double taxation' of C-corp structure.
Form 1120 is due April 15 for calendar-year filers, with an automatic six-month extension available via Form 7004 (October 15 extended due date). Fiscal-year C-corps file by the 15th day of the 4th month after year-end.
For owner-led businesses, the choice between C-corp (Form 1120) and S-corp (Form 1120-S) or LLC is almost always about tax cost, benefits eligibility, and future exit plans. C-corp makes sense for businesses that reinvest all profit for years, need to attract institutional investors, or fit the QSBS (Section 1202) fact pattern. It rarely makes sense for a profitable owner-operated service business that distributes cash to the owner every year.
Common pitfalls
- Electing C-corp for the 21% rate without modeling the second layer of tax on distributions — the combined burden is often higher than an S-corp
- Missing the April 15 deadline and racking up late-filing penalties even when the corp owes no tax
- Paying deductible-looking 'owner draws' out of a C-corp without formalizing them as salary or dividend — the IRS reclassifies and assesses back tax
- Not planning for accumulated-earnings tax when the corp piles cash and never distributes it
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