State-Level Wealth Tax Proposals and the California 2026 Billionaire Tax Initiative

State-Level Wealth Tax Proposals and the California 2026 Billionaire Tax Initiative

The policy debate over state-level wealth taxation in the United States has reached a critical empirical and technical milestone with the qualification of California's Proposition 40 (the 2026 Billionaire Tax Act) for the November 3, 2026, general election ballot. This initiative represents a first-of-its-kind, real-world attempt to levy a wealth tax at the subnational level in the United States.

The initiative proposes a one-time 5% wealth tax on California residents with a worldwide net worth exceeding $1 billion as of December 31, 2026. The tax is payable in annual installments of 1% over five years, with a 7.5% annual deferral charge. To prevent preemptive capital flight, the initiative includes a retroactive residency "lock-in" date of January 1, 2026—meaning that anyone residing in California on that date remains liable for the tax regardless of subsequent out-migration.

The empirical debate over Proposition 40 is highly polarized, characterized by a direct clash between two major studies published in 2026: a progressive analysis by the National Bureau of Economic Research (NBER) and a conservative analysis by the Hoover Institution.

The Proponents' Case: High Revenue, Minimal Income Tax Loss

Proponents of the tax, led by economists Jasper Boll, Emmanuel Saez, and Gabriel Zucman (2026), argue that the wealth tax is highly administrable, revenue-positive, and essential to address extreme wealth inequality and federal funding cuts. Their NBER working paper documents that California's billionaire wealth has grown by 144% from 2023 to 2025, reaching $2.3 trillion across 250 billionaires as of July 1, 2026 (equivalent to 52% of California's annual GDP).

The core of the proponents' case rests on several key empirical points:

1. Current Under-Taxation of Billionaires: Boll, Saez, and Zucman estimate that California billionaires pay an average of only 0.2% of their wealth in California individual income tax ($3.2 billion annually). The top 4 centi-billionaires (Larry Page, Sergey Brin, Mark Zuckerberg, and Jensen Huang) hold over $948 billion—about 41% of all California billionaire wealth—yet pay an average of just 0.07% of their wealth in state income tax. In 2019, 2020, and 2023, Page and Brin paid $0 in California individual income tax on their Alphabet wealth because Alphabet paid no dividends, they sold no stock, and they received only $1 in symbolic salary, despite their share of Alphabet's corporate profits exceeding $10 billion each over those three years.
2. Robust Revenue Scoring: The authors estimate that the 5% tax will collect $104 billion over five years (assuming a 10% avoidance/evasion rate). If the state successfully implements a Pareto extrapolation to capture "missing small billionaires" in the $1 billion to $4.5 billion range (who are often undercounted by Forbes), the tax base could expand to 620 billionaires, raising up to $128 billion.
3. Overestimated Income Tax Spillover: Proponents argue that opponents vastly overestimate the income tax revenue lost due to out-migration. Opponents assume a standard income-to-wealth ratio of 2.25% for billionaires. However, actual SEC transaction data shows that the top 3 California billionaires have a fiscal income-to-wealth ratio of only 0.38% on their company holdings. Because their realized taxable incomes are so low, losing them to other states results in a comparatively minor loss of state income tax revenue (estimated at $0.15 billion to $0.51 billion annually).

The Opponents' Case: Deeply Negative Net Present Value

Opponents of Proposition 40, led by Stanford/Hoover economists Benjamin Jaros and Joshua Rauh (2026) and Tax Foundation fellow Jared Walczak (2026), argue that the tax will act as an economic "disaster" that ultimately costs the state more than it collects.

The core of the opponents' case rests on the following empirical arguments:

1. Substantial Capital Flight Already Underway: Rauh and Jaros document that nearly 30% of the wealth tax base has already departed California in anticipation of the tax. They identify six high-profile billionaires—including Google co-founders Larry Page and Sergey Brin, PayPal co-founder Peter Thiel, and former Uber CEO Travis Kalanick—who reportedly established domicile elsewhere prior to the January 1, 2026, residency lock-in. Walczak's CalTax study identifies a total of nine billionaire departures, creating an estimated $2.77 billion recurring annual tax revenue loss for the state.
2. Dramatically Lower Wealth Tax Yield: Due to these confirmed departures and additional "stealth out-migration" calculated using an elasticity of $e=10$ derived from Swiss and Spanish wealth tax studies, Rauh and Jaros project that the 5% tax will collect only $40 billion over five years—less than half of the $100 billion projected by proponents.
3. Negative Net Present Value (NPV): Because the wealth tax is a one-time levy but the loss of high-earner income tax revenue is permanent and recurring, opponents calculate that the Net Present Value of Proposition 40 to California's state revenues is negative $24.7 billion. In their simulations, 71% of plausible outcomes produce a negative NPV.
4. Permanent Constitutional Infrastructure: Opponents also warn that Proposition 40 amends the California Constitution to lift the state's cap on taxing intangible personal property (such as stocks and bonds) with no sunset provision, effectively building the constitutional infrastructure for a permanent, recurring wealth tax.

Key Methodological and Empirical Parameters Under Debate

The stark divergence between the two camps ($100B+ positive vs. $24.7B negative) is driven by three key methodological differences: