A federal wealth tax is probably unconstitutional under current Supreme Court doctrine, though the question has never been directly decided. The core problem is the Constitution’s apportionment rule for “direct” taxes, which would force a wealth tax to be divided among states by population rather than by where wealth actually sits. The Sixteenth Amendment created an exception for income taxes, but at least four sitting justices have signaled they do not consider unrealized gains in net worth to be “income” at all. So whether a wealth tax is unconstitutional comes down to a classification fight the Supreme Court has so far refused to resolve.
The Apportionment Rule Is the Central Obstacle
Article I splits federal taxes into two categories with very different rules. Indirect taxes (duties, imposts, and excises) only have to be “uniform throughout the United States,” which means the same rate and terms everywhere.1LII / Legal Information Institute. Historical Background of the Taxing Power Direct taxes face a much harder requirement: Article I, Section 9 says “No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census.”2Cornell Law School. U.S. Constitution Annotated – Article I, Section 9, Clause 4 Each state’s share of the total revenue must match its share of the national population.
That rule is why a wealth tax collapses in practice. Imagine Congress wants to raise $100 billion through a wealth tax. Under apportionment, a state with 3% of the population owes $3 billion of that total, whether its residents hold 3% of the country’s taxable wealth or a fraction of 1%. Because billionaires cluster in a handful of states while people are spread more evenly, residents of lower-wealth states would face dramatically higher effective rates than residents of wealthier ones. Two people with identical $500 million portfolios could owe wildly different amounts depending on their zip codes. No legislature will enact that, which is why the apportionment rule functions as a prohibition rather than a procedural step.
The Supreme Court Already Decided Wealth Is Direct
The Framers never defined “direct tax” with precision, and early cases read the category narrowly. That changed in 1895. In Pollock v. Farmers’ Loan and Trust Co., the Supreme Court struck down a federal income tax and held that “taxes on real estate being indisputably direct taxes, taxes on the rents or income of real estate are equally direct taxes,” extending the same logic to personal property and the income it generates.3Justia U.S. Supreme Court Center. Pollock v. Farmers’ Loan and Trust Company, 158 U.S. 601 (1895)
Pollock is the precedent wealth-tax opponents rely on. If taxing the income flowing from property counts as a direct tax, taxing the property itself is even more clearly direct. A wealth tax reaches the principal — the underlying asset — rather than any flow of money off it. Under Pollock, that places it squarely in the apportioned category.
The Sixteenth Amendment Only Rescues Income Taxes
The country responded to Pollock by ratifying the Sixteenth Amendment in 1913. Its text 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.”4Legal Information Institute at Cornell Law School. 16th Amendment
The amendment solved the income problem. It did not touch anything else. For a wealth tax to escape apportionment, it has to count as a tax on “income.” And in Eisner v. Macomber, decided seven years after ratification, the Court defined income as “a gain, a profit, something of exchangeable value, proceeding from the property, severed from the capital” and “received or drawn by the recipient for his separate use, benefit and disposal.” The Court added that “mere growth or increment of value in a capital investment is not income.”5Justia U.S. Supreme Court Center. Eisner v. Macomber, 252 U.S. 189 (1920)
That is the realization requirement, and it sits directly in the path of a wealth tax. A wealth tax on net worth hits assets that have appreciated on paper but have not been sold. Under Eisner, that paper appreciation has not been “severed from the capital” and is therefore not income. If it is not income, the Sixteenth Amendment offers nothing, and the tax falls back under Pollock into the apportionment trap.
Supporters push back on two fronts. The amendment reaches income “from whatever source derived,” which they read as broad license to tax economic gains however structured. And they argue annual appreciation in asset value is functionally income to the owner, whether or not it has been cashed out. Those are the arguments any wealth tax defender would have to win in court.
What Moore v. United States Signaled in 2024
The Supreme Court had the chance to settle the realization question in 2024 and deliberately refused. Moore v. United States involved the Mandatory Repatriation Tax, which taxed American shareholders on the undistributed earnings of foreign corporations they partly owned. The Moores argued the tax hit income they had never actually received.
The Court upheld the tax on narrow grounds: Congress may attribute a corporation’s realized but undistributed income to its American shareholders, consistent with a long history of pass-through taxation of partnerships and similar entities. The corporation itself had already realized the income through business activity. The only question was attribution.6Supreme Court of the United States. Moore v. United States (2024)
The majority then went out of its way to leave the bigger question open. “To decide this case, we need not resolve that disagreement over realization. Those are potential issues for another day.”6Supreme Court of the United States. Moore v. United States (2024) The government even conceded during the case that “a hypothetical unapportioned tax on an individual’s holdings or wealth might be considered a tax on property, not income.”
The separate opinions are where the real forecast lives. Justice Barrett, joined by Justice Alito, wrote that the Sixteenth Amendment’s reference to income “derived” from a source “encompasses a requirement that income, to be taxed without apportionment, must be realized.” Justice Thomas, joined by Justice Gorsuch, went further, arguing that “Sixteenth Amendment ‘incomes’ include only income realized by the taxpayer.” Justice Jackson wrote the opposite, saying the “alleged requirement appears nowhere in the text of the Sixteenth Amendment.”6Supreme Court of the United States. Moore v. United States (2024)
So the current scorecard: four justices have said realization is constitutionally required, one has said it is not, and five have declined to say. Any federal wealth tax that reaches unrealized gains would force the issue, and its defenders would need to flip at least one of the five silent justices.
Congress Already Taxes Some Unrealized Gains
The strongest argument on the other side is that Congress already imposes mark-to-market taxes in narrow contexts, and courts have not disturbed them.
Section 1256 of the Internal Revenue Code requires holders of certain futures contracts and options to treat each position “as sold for its fair market value on the last business day of such taxable year” and pay tax on the resulting paper gain.7Office of the Law Revision Counsel. 26 U.S. Code 1256 – Section 1256 Contracts Marked to Market Similar rules apply to shareholders of certain foreign investment funds who elect that treatment under Section 1296.8Internal Revenue Service. Instructions for Form 8621 (12/2025) The most sweeping example is the expatriation tax under Section 877A: when a wealthy American renounces citizenship, all of their property is “treated as sold on the day before the expatriation date for its fair market value,” triggering tax on gains never realized through a sale.9Office of the Law Revision Counsel. 26 USC 877A – Tax Responsibilities of Expatriation It applies to individuals whose average annual income tax liability exceeded $206,000 over the prior five years or whose net worth is at least $2 million.10Internal Revenue Service. Expatriation Tax
Opponents treat these as narrow carve-outs with their own justifications. Futures contracts settle daily through a clearinghouse, so marking to market reflects an actual cash position. The expatriation tax is triggered by a one-time event, not imposed year after year on the same property. A broad annual levy on all assets held by wealthy individuals is a different kind of tax, and these targeted precedents may not be elastic enough to cover it.
Fifth Amendment Problems Even If Apportionment Is Cleared
Suppose a wealth tax somehow survives the direct-tax question. It still faces constitutional challenges under the Fifth Amendment.
The most practical is due process in valuation. The Due Process Clause prohibits deprivation of property “without due process of law.”11Cornell Law School. Fifth Amendment Publicly traded stock is easy to value. Private businesses, closely held partnerships, real estate portfolios, and art collections are not. Two qualified appraisers can reach valuations for the same private company that differ by tens of millions of dollars. If the IRS and a taxpayer disagree by $200 million on a private business, a 2% rate turns that disagreement into $4 million a year in disputed tax. Pending legislation tries to force compliance through steep penalties — a 30% penalty when reported value is 65% or less of the correct amount, rising to 50% for gross misstatements below 40% of correct value12U.S. Congress. H.R. 8085 – Ultra-Millionaire Tax Act of 2026 — but harsh penalties for misvaluation only sharpen the problem when the “correct” value is itself a judgment call.
A secondary argument invokes the Takings Clause, which requires “just compensation” when private property is taken for public use.13Legal Information Institute. Takings Clause – Overview A tax is not normally a taking, and the threshold is high. But at extreme rates compounding over a decade, a wealth tax could consume a meaningful portion of the underlying asset, especially one that grows slowly or not at all. That argument probably fails against modestly rated proposals but puts a practical ceiling on how aggressive the rate can be.
What This Means for Current Proposals
No federal wealth tax has ever been enacted, and the constitutional questions have never been directly litigated. The most prominent current bill, H.R. 8085, the Ultra-Millionaire Tax Act of 2026, was introduced in March 2026 and would impose a 2% annual tax on net assets above $50 million and a 3% tax on net assets above $1 billion, rising to 6% above $1 billion if certain conditions are met.12U.S. Congress. H.R. 8085 – Ultra-Millionaire Tax Act of 2026 A separate approach, the Billionaire Minimum Income Tax, would impose a 25% minimum tax on individuals with net worth above $100 million, calculated on total income including unrealized capital gains. By labeling the base “income,” proponents hope to park the levy inside the Sixteenth Amendment. But calling unrealized appreciation “income” does not make it so for constitutional purposes, and any such law would draw an immediate challenge.
Where that challenge lands depends almost entirely on classification. If the Court treats a wealth tax as a direct tax on property, apportionment kills it. If it treats annual appreciation as income under the Sixteenth Amendment, uniformity across states is a low bar and the tax likely survives. Moore v. United States told us the Court is split on exactly that question and willing to leave it unresolved as long as possible. The next wealth tax case will be writing on a largely blank slate, with four justices already on record that unrealized gains are not income the federal government can tax without apportionment.