The 16th Amendment to the United States Constitution gives Congress the power to tax income directly, at uniform rates nationwide, without dividing the tax bill among the states by population. Ratified on February 3, 1913, it reads in full: “The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration.”1Congress.gov. U.S. Constitution – Sixteenth Amendment That single sentence is the constitutional foundation for every federal income tax collected today.
The Problem the Amendment Fixed
The original Constitution made a broad federal income tax nearly impossible to run. Article I, Section 9 required that any direct tax be divided among the states in proportion to their populations.2Congress.gov. Article I Section 9 Congress would have had to set a total dollar amount and then hand each state a share based on its census count. A state with twice the population owed twice the total, whether its residents were wealthy or poor. That formula could not produce a uniform tax on what people actually earned.
Through most of the 19th century the federal government leaned on tariffs and excise taxes instead. Congress did impose an income tax during the Civil War, and it briefly survived legal challenge. Then in 1895, the Supreme Court in Pollock v. Farmers’ Loan & Trust Co. struck down a peacetime income tax, ruling that taxes on income from property were direct taxes and had to be apportioned by population.3Justia U.S. Supreme Court Center. Pollock v. Farmers Loan and Trust Co. Because apportionment made a broad income tax unworkable, Pollock effectively closed the door on one.
The 16th Amendment reopened it. By removing the apportionment requirement for income taxes specifically, it let Congress tax earnings at the same rates in every state based on how much a person earned. Within months of ratification, Congress passed the Revenue Act of 1913, which set a 1 percent tax on net personal income above $3,000 and a surtax reaching 6 percent on incomes above $500,000.4Internal Revenue Service. Historical Highlights of the IRS Those rates look small now, but the framework has held ever since.
What “From Whatever Source Derived” Reaches
The amendment’s language is deliberately wide. Congress carried that breadth into statute at 26 U.S.C. ยง 61, which defines gross income as “all income from whatever source derived” and lists fourteen categories, including compensation for services, business profits, interest, rents, royalties, and dividends.5Office of the Law Revision Counsel. 26 USC 61 – Gross Income Defined That list is not exhaustive. Any measurable economic gain generally falls within its reach unless Congress has carved out a specific exclusion.
The practical result is broad. Your paycheck, freelance income, bank interest, stock dividends, rental profits, gambling winnings, prizes, and the value of bartered goods are all taxable. So is forgiven debt in most situations, because the cancellation leaves you better off than you were before. The source doesn’t matter. A traditional job, a side hustle, cryptocurrency trading, a night at a casino: if it increased your wealth, it starts as taxable income.
Income Congress Has Chosen to Exclude
The same power that lets Congress tax income lets it exempt categories of income. These statutory exclusions are scattered through the Internal Revenue Code and affect millions of taxpayers.
- Gifts and inheritances are generally not counted in gross income. Any income the property later generates (rent, dividends, interest) is taxable, but the value you receive is not. For 2026, a donor can give up to $19,000 per recipient per year without triggering a gift tax filing.6Office of the Law Revision Counsel. 26 USC 102 – Gifts and Inheritances
- Life insurance death benefits paid because the insured person died are excluded from gross income, whether paid as a lump sum or in installments. Exceptions apply when a policy was transferred for value before death.7Office of the Law Revision Counsel. 26 USC 101 – Certain Death Benefits
- Interest on bonds issued by state and local governments is typically exempt from federal income tax, which is why municipal bonds pay lower yields than comparable taxable investments.
- Employer-paid health insurance premiums, contributions to qualifying retirement accounts, and certain fringe benefits are excluded or deferred under various Code sections.
These are policy choices, not constitutional rights. Congress can narrow or eliminate any of them by legislation.
How the Amendment Works Today
The 16th Amendment supplies the authority; the Internal Revenue Code under Title 26 supplies the rules. Congress sets rates, defines deductions, and creates credits. The IRS, operating under the Secretary of the Treasury, administers and enforces them.8Internal Revenue Service. About the Internal Revenue Service – Section: Statutory Authority
The federal income tax runs on a progressive structure with seven marginal rates. For 2026, a single filer’s taxable income is taxed as follows:9Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
- 10 percent on income up to $12,400
- 12 percent from $12,401 to $50,400
- 22 percent from $50,401 to $105,700
- 24 percent from $105,701 to $201,775
- 32 percent from $201,776 to $256,225
- 35 percent from $256,226 to $640,600
- 37 percent above $640,600
These are marginal rates. Only income within each bracket is taxed at that bracket’s rate. Someone earning $60,000 does not pay 22 percent on the whole amount: the first $12,400 is taxed at 10 percent, the next portion at 12 percent, and only the slice above $50,400 hits 22 percent.
Before applying those rates, most taxpayers reduce taxable income by claiming either the standard deduction or itemized deductions. The 2026 standard deduction is $16,100 for single filers and $32,200 for married couples filing jointly.9Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 That deduction alone means a single filer earning under $16,100 owes no federal income tax.
Challenges to the Amendment and Why They Fail
People have argued the 16th Amendment is invalid, unenforceable, or narrower than Congress claims almost since ratification. Federal courts have rejected every one of these arguments.
The Supreme Court addressed the amendment’s scope three years after ratification in Brushaber v. Union Pacific Railroad (1916). The Court held that the amendment’s purpose was to free income taxes from apportionment, and that it did not create a new taxing power but removed the procedural obstacle Pollock had erected. The amendment, the Court wrote, was meant “to relieve all income taxes when imposed from apportionment from a consideration of the source whence the income was derived.”
A recurring line of attack claims the amendment was never properly ratified because some states approved slightly different text or because procedural steps were flawed. Courts reject these arguments under the enrolled bill doctrine, which holds that once the required number of states have ratified and the Secretary of State has certified the amendment, courts will not go behind that certification to hunt for clerical errors in state records. Federal appellate courts have called these arguments frivolous.
More recently, in Moore v. United States (2024), the Supreme Court upheld the Mandatory Repatriation Tax, which taxed American shareholders on accumulated foreign corporate profits they had not received as distributions. The Moores argued the tax violated the 16th Amendment because they had not “realized” the income. The Court ruled that Congress could attribute a corporation’s realized income to its shareholders and tax them on it. It declined to decide whether the Constitution requires income to be realized before it can be taxed, leaving that question open.10Supreme Court of the United States. Moore v. United States
Bringing a frivolous challenge to the income tax carries a price. The Tax Court can impose sanctions of up to $25,000 when a taxpayer’s position is frivolous or groundless, or when the case was filed primarily to delay collection.11Office of the Law Revision Counsel. 26 USC 6673 – Sanctions and Costs Awarded by Courts The IRS keeps a public list of arguments it treats as frivolous, and courts treat positions on that list as forfeited from the start. Whatever debates exist about the American tax system, the constitutional authority behind the income tax is settled.