Sixteenth Amendment — Federal Income Tax

The Sixteenth Amendment, ratified in 1913, authorizes Congress 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." With thirty-five words, it overturned the Supreme Court's 1895 decision in Pollock v. Farmers' Loan & Trust Co., which had struck down a federal income tax as an unconstitutional direct tax requiring apportionment, and cleared the constitutional path for the modern federal tax system. The result is the Internal Revenue Code — a $5 trillion-per-year revenue machine that funds virtually every federal program and shapes nearly every financial decision Americans make. Understanding the amendment's scope, the breadth of "income from whatever source derived," and the constitutional limits on Congress's taxing power is foundational to understanding U.S. fiscal policy.

Current Law (2026)

Key Mechanics

The Sixteenth Amendment (ratified February 3, 1913) authorized Congress to levy an income tax without apportionment among the states — removing the constitutional obstacle that had invalidated the 1894 federal income tax in Pollock v. Farmers' Loan & Trust Co. (1895). Under the original Constitution, "direct taxes" had to be apportioned by population; Pollock held that a tax on income from property (rents, dividends, interest) was a direct tax subject to apportionment, making a federal income tax practically impossible. The Sixteenth Amendment eliminated this constraint for income taxes: Congress may tax "incomes, from whatever source derived" without any apportionment requirement. The constitutional definition of "income" has evolved through case law: Eisner v. Macomber (1920) defined income as "gain derived from capital, from labor, or from both combined" — suggesting a realization requirement; Glenshaw Glass (1955) broadened the definition to "undeniable accessions to wealth, clearly realized, and over which the taxpayers have complete dominion" — the modern standard. Statutory implementation: 26 U.S.C. § 61 defines gross income as "all income from whatever source derived" with a non-exhaustive list of 15 categories; courts and the IRS have applied this expansively. The realization requirement — whether income must be "realized" before it can be taxed — remains the central unsettled constitutional question: Moore v. United States (2024) upheld the Mandatory Repatriation Tax on undistributed foreign corporate earnings, but the Court explicitly declined to resolve whether the Sixteenth Amendment requires realization, leaving open the constitutional permissibility of wealth taxes and mark-to-market taxation. The Amendment does not impose any maximum rate — the current top individual rate is 37%; the highest historical rate was 94% (1944–1945).

Legal Authority

• U.S. Const. amend. XVI — "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."
• U.S. Const. art. I, § 8, cl. 1 — General taxing and spending power: "The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States"
• U.S. Const. art. I, § 2, cl. 3; art. I, § 9, cl. 4 — Direct tax apportionment requirement (superseded for income taxes by the Sixteenth Amendment)
• 26 U.S.C. § 61 — Statutory definition of gross income: "all income from whatever source derived," including compensation, business profits, capital gains, dividends, rents, royalties, alimony, gambling winnings, and cancellation of debt
• 26 U.S.C. § 1 — Individual income tax rates, brackets, and filing statuses
• 26 U.S.C. § 7201 — Criminal penalty for willful tax evasion (felony, up to 5 years imprisonment)
• Eisner v. Macomber, 252 U.S. 189 (1920) — Defined income as gain "derived from capital, from labor, or from both combined" — established that a mere stock dividend (no realized gain) is not taxable income
• Commissioner v. Glenshaw Glass Co., 348 U.S. 426 (1955) — Broadened the definition: income includes "undeniable accessions to wealth, clearly realized, and over which the taxpayers have complete dominion" — settled the modern broad interpretation of § 61
• Moore v. United States, 602 U.S. 572 (2024) — Upheld the Mandatory Repatriation Tax (§ 965) on undistributed foreign corporate earnings; the Court declined to resolve whether the Sixteenth Amendment requires realization, but preserved the tax on narrow grounds

How It Works

The Pre-Amendment Problem: Pollock and Apportionment

The original Constitution permitted direct taxes only if apportioned among the states by population. Article I, § 9, clause 4 reflected Founding-era concerns about taxing wealth held in property — Southern states feared Congress would tax slave-holding wealth. When Congress enacted a 2% income tax in 1894 during the second Cleveland administration (the Wilson-Gorman Tariff Act), the Supreme Court struck it down in Pollock v. Farmers' Loan & Trust Co. (1895) as a direct tax requiring apportionment. The decision was devastating: an unapportioned income tax was simply unconstitutional. Because apportioning an income tax by state population would mean Wyoming residents paying far higher rates than New York residents (relative to income), an apportioned income tax was practically unworkable. The federal government remained dependent on tariffs and excise taxes — regressive taxes that fell disproportionately on ordinary consumers.

The progressive movement of the early twentieth century, backed by President Taft and a bipartisan coalition in Congress, pushed for a constitutional amendment. The Sixteenth Amendment was proposed in 1909 and ratified in 1913 — the same year Congress enacted the modern income tax and the Federal Reserve Act was signed. Together these reforms fundamentally restructured American fiscal capacity.

What the Amendment Authorizes

The amendment grants Congress power to tax income without apportionment. The critical interpretive questions have been: (1) What is "income"? and (2) Must income be "realized" before it is taxable?

Breadth of "income": Section 61 of the Internal Revenue Code defines gross income as "all income from whatever source derived" and then lists 15 examples. Courts have interpreted this expansively. Under Glenshaw Glass (1955), income includes any "undeniable accession to wealth, clearly realized, and over which the taxpayer has complete dominion." This covers wages, salaries, tips, interest, dividends, rents, royalties, business profits, capital gains, gambling winnings, prizes, treasure trove, cancellation of debt (generally), and most other forms of economic benefit. Congress creates exclusions from income by statute — employer-provided health insurance (§ 106), municipal bond interest (§ 103), gifts and inheritances (§ 102), life insurance death benefits (§ 101) — but absent a statutory exclusion, the default is inclusion.

The realization requirement: Eisner v. Macomber (1920) held that a stock dividend — additional shares of the same stock — was not taxable income because no value was realized. The shareholder's proportionate interest in the corporation hadn't changed; no cash or new asset had been received. Macomber was read as constitutionally requiring realization before taxation — the amendment only authorized taxing realized gains, not paper appreciation. Congress has generally honored a realization requirement in the Internal Revenue Code (§ 1001: gain recognized on sale or exchange). But the constitutional necessity of realization has been debated for decades, and Moore v. United States (2024) brought it to a head.

Moore v. United States (2024): The Tax Cuts and Jobs Act of 2017 enacted § 965, the Mandatory Repatriation Tax (MRT), a one-time tax on undistributed accumulated profits of controlled foreign corporations — taxing shareholders on corporate income that had never been distributed as dividends. Charles and Kathleen Moore, who owned shares in an Indian agricultural company, challenged the MRT as unconstitutional because they had never received a distribution; no gain had been "realized." The Supreme Court upheld the MRT 7-2, but the majority opinion by Justice Jackson explicitly declined to resolve whether realization is a constitutional requirement for income taxation. The Court held that Congress may tax income attributed from controlled entities to their shareholders — a settled practice extending to partnerships, S corporations, and CFCs — and that the MRT fell within this tradition. Justices Barrett and Alito, joined by Justice Thomas in dissent, argued the Court should have squarely ruled on realization. The constitutional question whether Congress could enact a wealth tax — taxing unrealized appreciation on assets — remains open. The Biden-era billionaire minimum income tax proposals and Democratic proposals to tax unrealized capital gains would directly implicate Pollock-era apportionment concerns if not within the amendment's scope, or would require their own constitutional amendment.

Structural Features of the Income Tax

The current income tax is a progressive rate structure: ordinary income is taxed at graduated rates (10%, 12%, 22%, 24%, 32%, 35%, 37%) that increase as income rises. Capital gains — profits from selling appreciated assets held more than one year — are taxed at preferential rates (0%, 15%, 20%) under a longstanding policy preference for investment. The alternative minimum tax (AMT) runs parallel to the regular tax and prevents high earners from using too many preferences to eliminate tax liability (§ 55–59). The standard deduction (in 2026: $16,100 single / $32,200 married filing jointly, reflecting OBBBA's permanent boost) and itemized deductions reduce taxable income. The earned income tax credit, child tax credit, and other refundable credits can reduce tax liability below zero — functioning as targeted income support through the tax system.

The Sixteenth Amendment authorizes taxation of income but does not itself impose a tax. Congress has plenary authority to define income, set rates, create exclusions and deductions, and impose alternative regimes. The constitutional limit is that (1) the tax must be on "income" as that term is understood under the amendment (the Macomber/Glenshaw Glass framework), and (2) if Congress wishes to tax something that is arguably a "direct tax" rather than an income tax, apportionment by population is still required unless the Sixteenth Amendment covers it. As a practical matter, every tax challenged as an unapportioned direct tax in the last century has been upheld either as an income tax or as an indirect tax (excise).

Tax Protesters and Frivolous Arguments

Federal courts have repeatedly — and uniformly — rejected arguments that the Sixteenth Amendment was never properly ratified, that the income tax is voluntary, that wages are not income, that citizens are not subject to income tax, or that filing a tax return violates the Fifth Amendment. These arguments are legally frivolous. The amendment was ratified by the required number of states. Willful failure to file a tax return is a misdemeanor (§ 7203); willful tax evasion is a felony (§ 7201) punishable by up to five years' imprisonment. The IRS and courts impose significant penalties on taxpayers who advance frivolous positions (§ 6702: $5,000 penalty for frivolous returns; § 6673: up to $25,000 sanctions in Tax Court for frivolous proceedings).

How It Affects You

If you are an individual employee or wage earner: The Sixteenth Amendment is the constitutional foundation for everything on your W-2 and Form 1040. Your employer is required by law to withhold federal income tax from each paycheck and remit it to the IRS (§ 3402). At year's end, you reconcile withholding against actual tax liability. You owe tax on all wages, salaries, tips, interest, dividends, and most other income — the legal burden of proof that something is excluded is yours, not the IRS's. The progressive rate structure means your marginal rate (on the last dollar earned) is higher than your effective rate (average rate on all income). Common tax reduction strategies for employees include maxing out pre-tax 401(k) contributions (reducing gross income), claiming the standard or itemized deduction, and using the earned income tax credit or child tax credit if eligible.

If you are a business owner, investor, or entrepreneur: The Sixteenth Amendment's breadth reaches all business income, pass-through income (partnerships, S corporations, and sole proprietors report on Schedule C, E, or F), capital gains from selling your company or investments, and dividends. The preferential capital gains rate (maximum 20%, plus 3.8% net investment income tax for high earners under § 1411) creates significant incentives around asset holding periods and exit structuring. The TCJA's Qualified Business Income deduction (§ 199A) allows pass-through business owners to deduct up to 20% of qualified business income — reducing effective rates for many entrepreneurs. Corporate owners face the double-taxation structure: the corporation pays 21% corporate income tax, then shareholders pay tax again on dividends. Understanding whether business income is ordinary (top rate 37% + self-employment tax) or capital gain (top rate 23.8%) is central to tax planning at exit.

If you are a tax attorney, CPA, or financial planner: The constitutional questions left open by Moore v. United States (2024) — particularly whether realization is a constitutional requirement for income taxation — are the most significant open questions in tax law. Democratic proposals for a mark-to-market tax on billionaires' unrealized gains, a minimum income tax on wealthy individuals, or a wealth tax (as proposed by Senators Warren and Sanders) would face constitutional challenges: either they are within the Sixteenth Amendment's scope (taxing "income from whatever source derived") without a realization requirement, or they are direct taxes requiring apportionment, making them effectively unconstitutional. Advising clients on estate planning, charitable giving, and retirement distributions all require navigating the Sixteenth Amendment's boundaries in ways that appear in § 61 exclusions (§ 102 gifts, § 101 life insurance), deferral provisions (§ 401-408 retirement accounts), and recognition events (§ 1001).

If you are a student of constitutional history or policy: The Sixteenth Amendment is a case study in constitutional change through formal amendment — the Amendment process working as designed. The Pollock decision created a structural problem (the federal government couldn't tax income at graduated rates to fund the growing demands of the twentieth century) that the political process resolved through Article V. The amendment's ratification in 1913 — the same year as the Federal Reserve Act — fundamentally altered the balance between the federal government's fiscal capacity and the states. Without the Sixteenth Amendment, the twentieth century's massive federal programs — Social Security, Medicare, Medicaid, the interstate highway system, federal education funding, national defense — could not have been funded without apportionment, a practical impossibility. The amendment is also a reminder that constitutional interpretation matters: Pollock narrowly read "direct taxes" to doom the income tax; the amendment eliminated that constraint by name.

State Variations

The Sixteenth Amendment authorizes federal income taxation only — it does not directly govern state income taxes. States derive their authority to tax income from their own constitutions and statutes, and their tax systems vary enormously:

States with no income tax: Alaska, Florida, Nevada, New Hampshire (on wages; interest and dividend tax repealed 2025), South Dakota, Tennessee, Texas, Washington (on wages; a capital gains tax exists), and Wyoming impose no broad-based income tax on wages. Residents of these states pay federal income tax but no state income tax — a significant financial advantage for high earners who can relocate.

States with flat income taxes: Arizona (2.5% flat), Colorado (4.4%), Georgia (5.49% moving to 4.99%), Idaho (5.8%), Illinois (4.95%), Indiana (3.05%), Kentucky (4.0%), Michigan (4.25%), Mississippi (4.7% moving to 4% by 2026), North Carolina (4.5%), Pennsylvania (3.07%), and Utah (4.55%) impose a single rate on all income levels. Flat tax states argue their systems are simpler and less economically distortionary.

States with progressive taxes: California (top rate 13.3%), Hawaii (top rate 11%), Oregon (top rate 9.9%), Minnesota (top rate 9.85%), New York (top rate 10.9%), New Jersey (top rate 10.75%), and Vermont (top rate 8.75%) impose rates that increase with income — paralleling the federal structure but using different brackets and bases. High earners in these states can face combined federal + state marginal rates exceeding 50%.

Conformity to federal law: Most states "conform" to federal definitions of income either on a "rolling" basis (automatically adopting federal changes) or a "static" basis (conforming to the federal code as of a specific date). This means federal tax changes ripple into state tax systems, often requiring states to "decouple" from specific federal provisions they don't wish to adopt. The TCJA's changes to § 199A, § 163(j), § 174, and bonus depreciation created significant state conformity decisions in 2018-2026.

Pending Legislation

• Billionaire Minimum Income Tax / Unrealized Gains Proposals: Democratic proposals in the 118th and 119th Congresses to tax unrealized capital gains on assets held by ultra-high-net-worth individuals have not advanced, but remain a live policy debate. Their constitutionality under the Sixteenth Amendment — specifically whether taxing unrealized appreciation is taxing "income" — would likely be challenged. Moore (2024) declined to resolve the realization question.
• Flat Tax Proposals: Republican members have repeatedly introduced legislation to replace the progressive income tax with a flat tax or a national consumption tax. The FairTax Act (H.R. 25 / S. 122) would replace the income tax with a 30% national sales tax and require repeal of the Sixteenth Amendment (the bill itself includes such a call). No floor vote has occurred.
• OBBBA made TCJA individual provisions permanent (July 4, 2025): The One Big Beautiful Bill Act (Pub. L. 119-21, signed July 4, 2025) made permanent most of the TCJA individual tax provisions that had been scheduled to expire at the end of 2025 — including the lower marginal rates, the higher standard deduction, the 20% Qualified Business Income deduction, and the AMT exemption increases — and made additional changes that took effect for the 2026 tax year. The estate tax exemption was set at $15 million per individual permanently.

Recent Developments

• 2024 — Moore v. United States: The Supreme Court upheld the Mandatory Repatriation Tax (§ 965) on a narrow ruling, declining to resolve whether the Sixteenth Amendment requires realization. The 7-2 decision preserved the existing income tax system while leaving the constitutional door open to future challenges on wealth taxes and mark-to-market proposals. Justice Barrett's concurrence questioned whether Eisner v. Macomber's realization holding remains good law.
• 2025-2026 — OBBBA permanent extension: The One Big Beautiful Bill Act (signed July 4, 2025) made TCJA's individual provisions permanent through budget reconciliation, locking in the lower rates, higher standard deduction, doubled-then-$15M estate exemption, and 20% QBI deduction.
• 2025 — IRS Direct File Expansion: The IRS expanded its Direct File program (free federal tax filing directly with the IRS) to all 50 states. The program allows eligible taxpayers (primarily those with simple W-2 income) to file federal returns at no cost without using private tax software. Tax preparation companies challenged the program's legality; the administration defended it under IRS's broad statutory authority.
• 2024-2025 — State Flat Tax Conversions: Several states moved from progressive income taxes to flat-rate systems, responding to competition for high-income residents and businesses. Georgia, Iowa, and Mississippi accelerated flat tax phase-ins; North Carolina continued its rate reductions toward a near-zero income tax. This state-level experiment in flat-rate taxation affects migration patterns and provides a policy comparison point for federal flat tax debates.
• 2025 — Wealth Tax Litigation (State Level): Washington State's capital gains tax (on gains above $250,000, enacted 2021) survived a state constitutional challenge in Quinn v. State (Wash. 2023). California voters rejected a wealth surtax measure. These state-level experiments inform federal constitutional analysis, though state constitutional constraints differ from the Sixteenth Amendment's federal framework.