A C-corporation is the default corporate form and a separate taxpayer in its own right. It pays a flat 21% federal tax on its profit, and then the owner pays tax again on any dividend — the double taxation that makes the C-corporation a poor fit for a business that simply distributes its earnings to its owner.
A corporation is C by default and S only by affirmative election on Form 2553. An LLC, however, defaults to partnership or disregarded treatment; to be taxed as a C-corporation without changing its legal form, an LLC files Form 8832 (the check-the-box election) to elect association status. This matters when you want C-corporation tax treatment for fringe-benefit or QSBS reasons but prefer to keep the LLC’s operational and state-law flexibility. The election can be effective up to 75 days retroactive or any prospective date you specify, and once made cannot be revoked for five years without IRS consent.
The one mandatory case. A business that intends to issue qualified small business stock (section “Qualified Small Business Stock”) must be a C-corporation. The IRC §1202 exclusion applies only to stock of a domestic C-corporation, and the holding clock starts on the date the corporation is formed or the date an LLC is converted (typically tax-free under IRC §351, “Transfer to corporation controlled by transferor”). A founder who began as an LLC and waited until a financing round to convert has lost years of QSBS-clock time and may have given up the exclusion entirely.
The fringe-benefit play. The C-corporation is the only entity in which an owner can receive fully deductible employer-paid fringe benefits as an employee, without the disqualifying 2-percent-owner rules that govern S-corporations. Health insurance premiums, group-term life insurance up to $50,000 of coverage, dependent-care assistance, qualified educational assistance, and accident and disability premiums are all deductible to the corporation and excludable from the owner-employee’s W-2. For an owner who would otherwise pay these out of post-tax dollars, the structural saving can outweigh the double-tax cost on retained earnings. The play breaks down once dividends are paid: the second layer of tax extinguishes the saving. It works best for a C-corporation that is retaining and reinvesting most of its earnings.
The accumulated-earnings problem. A C-corporation that retains earnings beyond the reasonable needs of its business attracts the IRC §531, “Accumulated earnings tax” accumulated-earnings tax: a 20% surcharge on the excess, on top of the regular 21% corporate rate. “Reasonable needs” covers working capital, planned expansion, debt retirement, and contingency reserves — documented. The first $250,000 of accumulated earnings ($150,000 for personal-service corporations) is a safe harbor. Above that level, document every dollar of retained cash against a specific business purpose in board minutes and the annual operating plan: working-capital reserve sized to actual operating needs, an expansion budget tied to identified opportunities, a debt-repayment schedule, contingency reserves tied to identified risks. With that paper trail the IRS rarely sustains a deficiency; without it, a small C-corporation that has been holding cash for several years is a standard audit target and the deficiency is usually conceded once examined.
A parallel concern is the IRC §541, “Personal holding company tax” personal holding company tax, another 20% surcharge applied to a closely held C-corporation whose income is concentrated in passive sources (dividends, interest, rents, royalties). Keep passive investments outside the operating C-corporation. Portfolio assets belong in personal accounts or in a separate investment-only structure (a family LLC, a personal holding partnership) — never sitting on the operating company’s balance sheet alongside the working capital.
When C-corp is wrong. For a service business that distributes most of its earnings to the owner and has no realistic exit, the C-corporation is a structural mistake. Every dollar of profit is taxed at 21% inside the corporation, then again at qualified-dividend rates (up to 23.8% with NIIT) when distributed — a combined federal effective rate near 40%, before state tax. The same dollar of profit in an S-corporation flows through to the owner once at the owner’s marginal rate. The C-corp default is for businesses that retain and compound earnings, not for businesses that pay them out.