Corporate income tax is a federal tax on the net profits of businesses organized as C-corporations, charged at a flat 21% of taxable income, with most states adding their own tax on top. Because a corporation is a legal person separate from its owners, the company files its own return and pays the tax before any profit reaches shareholders. That separation is what produces the familiar “double taxation” problem: the corporation pays once on its earnings, and shareholders pay again on dividends they receive from what’s left.
Which Businesses Owe It
The tax falls on C-corporations. Any business that files articles of incorporation with a state is a C-corporation by default unless it files Form 2553 with the IRS to elect S-corporation status.1Internal Revenue Service. Filing Requirements for Filing Status Change The S election has eligibility limits, including a cap of 100 shareholders and a requirement that all shareholders be U.S. individuals or certain trusts. Companies that miss the window or don’t qualify remain C-corporations and owe corporate income tax at the entity level.
Pass-through entities skip this tax entirely. S-corporations, partnerships, and sole proprietorships push their profits directly onto the owners’ personal returns, where the income is taxed once at individual rates. Large and publicly traded companies stay C-corporations because the shareholder restrictions on S status make it impractical at scale.
How Taxable Income Is Calculated
Corporate taxable income is gross income minus allowable deductions.2Office of the Law Revision Counsel. 26 USC 63 – Taxable Income Defined Gross income captures everything the corporation earns during the year: sales, service revenue, interest, rents, royalties, and gains on asset sales. From that, the corporation subtracts ordinary business expenses like wages, rent, insurance, supplies, and interest on business debt. What remains is what actually gets taxed.
Two deduction rules shape that number more than most.
Depreciation and Section 179
When a corporation buys equipment, vehicles, or other tangible property, it generally can’t deduct the full cost in year one. It spreads the deduction over the asset’s useful life under the Modified Accelerated Cost Recovery System.3Office of the Law Revision Counsel. 26 USC 168 – Accelerated Cost Recovery System MACRS assigns each type of property a recovery period: five years for computers and vehicles, seven years for office furniture, 39 years for commercial buildings.
Section 179 is the alternative. A corporation can deduct the entire cost of qualifying equipment and software in the year it’s placed in service, up to a limit. For 2026, that limit is $2,560,000, and it phases out dollar-for-dollar once total equipment purchases exceed $4,090,000. Section 179 pulls the tax benefit into the current year instead of stretching it across a decade.
Business Interest Deduction Limits
Corporations can’t always deduct every dollar of interest they pay. Under Section 163(j), business interest expense is capped at 30% of adjusted taxable income plus business interest income for the year.4Internal Revenue Service. Questions and Answers About the Limitation on the Deduction for Business Interest Expense Interest above the cap isn’t lost; it carries forward. The rule mostly bites on highly leveraged companies and acquisition-heavy balance sheets.
The Federal Rate
The federal government taxes all corporate taxable income at a flat 21%.5Office of the Law Revision Counsel. 26 USC 11 – Tax Imposed There are no graduated brackets at the corporate level. A company with $50,000 of taxable income and one with $50 million pay the same rate on each dollar.
Credits can drop the actual bill below what 21% would produce. The research and development credit, claimed on Form 6765, rewards spending on qualifying research by cutting the tax owed dollar-for-dollar.6Internal Revenue Service. About Form 6765, Credit for Increasing Research Activities That direct offset makes credits far more valuable than deductions, which only reduce taxable income.
The Corporate Alternative Minimum Tax
The Inflation Reduction Act of 2022 added a second layer for the largest corporations. Companies with average annual adjusted financial statement income of $1 billion or more must pay a 15% corporate alternative minimum tax on that book income when it exceeds what they’d owe at the regular 21% rate.7Internal Revenue Service. Corporate Alternative Minimum Tax The rule targets corporations that report large profits to shareholders but shrink taxable income through deductions and credits. Small and mid-size corporations don’t come close to the threshold.
State Corporate Income Tax
Most states impose their own corporate income tax on top of the 21% federal rate. State rates range from zero in Nevada, South Dakota, Texas, Washington, and Wyoming to as high as 11.5% at the top marginal bracket. The median top rate across states that tax corporate income sits around 6.5%. Some states use flat rates, others use graduated brackets. A few states without a traditional corporate income tax still charge gross receipts or franchise taxes that function similarly.
A corporation only owes a state that has “nexus” over it: a sufficient connection to the jurisdiction. Physical presence (an office, a warehouse, employees) has always created nexus, but many states now assert economic nexus based on sales volume alone. A company selling into a state where it has no office or staff can still owe corporate tax there if its revenue crosses the state’s threshold. Multi-state corporations also have to divide their taxable income among the states where they operate, and each state has its own apportionment formula built on some mix of sales, payroll, and property.
Double Taxation on Corporate Profits
The same profit gets taxed twice. First the corporation pays 21% on its net income. Then, when the corporation distributes what’s left as dividends, shareholders owe individual income tax on those payments. The IRS tracks the distributions through Form 1099-DIV, which reports dividend income to both the shareholder and the government.8Internal Revenue Service. About Form 1099-DIV, Dividends and Distributions
The qualified dividend rate softens the blow. Instead of ordinary income rates (up to 37% for individuals in 2026), qualified dividends from domestic corporations are taxed at the long-term capital gains rates of 0%, 15%, or 20% depending on the shareholder’s taxable income. For a single filer in 2026, the 0% rate applies to taxable income up to $49,450, the 15% rate covers $49,450 to $545,500, and 20% kicks in above that. Joint filers see corresponding thresholds of $98,900 and $613,700.
The combined burden is still real. A dollar of corporate profit taxed at 21% leaves 79 cents. If a shareholder in the 15% bracket receives that 79 cents as a qualified dividend, another 11.85 cents goes to individual tax, leaving about 67 cents. Pass-through entities avoid this stack by taxing the income once at the owner’s rate, which is the cost businesses weigh against the other benefits of incorporating.
Net Operating Loss Carryforwards
A losing year isn’t dead weight. A net operating loss can carry forward to reduce taxable income in future profitable years. For losses arising after 2017, the deduction is capped at 80% of taxable income in the year the loss is applied.9Internal Revenue Service. Instructions for Form 172 The other 20% of that year’s income is taxed normally, so the government still collects from a recovering company. Post-2017 losses carry forward indefinitely, but they can no longer be carried back to generate refunds from prior years, with narrow exceptions for certain farming losses.
Losses from tax years before 2018 follow the older rules: two-year carryback, 20-year carryforward, no 80% cap. Corporations still holding pre-2018 losses apply those first, without the percentage limit, before using anything from 2018 or later.
Quarterly Estimated Payments
Corporations don’t wait until the filing deadline to pay. Any corporation expecting a tax liability of $500 or more for the year must make quarterly estimated tax payments.10Office of the Law Revision Counsel. 26 USC 6655 – Failure by Corporation to Pay Estimated Income Tax For calendar-year filers, the four installments are due April 15, June 15, September 15, and January 15 of the following year.11Internal Revenue Service. Estimated Tax – Top Frequently Asked Questions
Underpaying triggers a penalty. The IRS charges what amounts to interest on the shortfall when a corporation doesn’t pay the lesser of its current-year or prior-year liability on time. First-year corporations often trip here, discovering the quarterly obligation only when they file the first return and see the penalty attached.
Filing the Return
Every C-corporation files its annual return on Form 1120, the U.S. Corporation Income Tax Return.12Internal Revenue Service. Instructions for Form 1120, U.S. Corporation Income Tax Return Calendar-year corporations must file by April 15. Fiscal-year corporations file by the 15th day of the fourth month after their tax year ends.13Office of the Law Revision Counsel. 26 USC 6072 – Time for Filing Income Tax Returns Filing Form 7004 before the deadline grants an automatic six-month extension to file.14Internal Revenue Service. About Form 7004, Application for Automatic Extension of Time to File Certain Business Income Tax, Information, and Other Returns The extension covers filing, not payment. Any tax owed is still due on the original date, and interest runs on unpaid balances from then.
Penalties for missing the deadlines are steep. The failure-to-file penalty is 5% of unpaid tax per month or partial month the return is late, capped at 25%.15Internal Revenue Service. Failure to File Penalty A separate failure-to-pay penalty of 0.5% per month runs on any tax not paid by the due date, also capped at 25%. When both apply in the same month, the IRS reduces the failure-to-file penalty by the failure-to-pay amount so the combined rate stays at 5% for that period. The takeaway: file on time even if you can’t pay in full, because the filing penalty is ten times steeper than the payment penalty.