Billionaire Tax Backfires – Billions Vanish

California’s one-time 5% “billionaire tax” could backfire and leave the state tens of billions poorer, according to new estimates.

Story Highlights

Supporters project about $100 billion over five years from a 5% tax on billionaire wealth.
Stanford economists estimate only about $30 billion would be collected.
Seven public billionaire departures removed roughly $540 billion from the tax base.
Lost income-tax revenue could exceed proceeds by about $39 billion.

What Proposition 40 Would Do and Who Pays

California voters will decide whether to approve Proposition 40, a one-time wealth tax on residents who were billionaires on January 1, 2026. The measure would apply a 5% levy on worldwide wealth, paid in five annual 1% installments starting after 2026. Supporters say about 250 taxpayers would owe the tax, and the money would help replace expected federal cuts to health care and other programs. The structure and tax base allow formal modeling of likely receipts.

Berkeley-affiliated economists estimate that taxable wealth totals about $2.307 trillion. Their model applies the 5% rate to reach about $115 billion, then subtracts 10% for tax avoidance and evasion. The result is about $104 billion, which they round to $100 billion. They describe the tax as one-time, with collections spread across five years. Backers say this approach targets a small number of ultra-wealthy residents to meet an urgent funding need without raising broad taxes.

Why Critics Say The Math Does Not Pencil Out

Stanford economists Benjamin Jaros and Joshua Rauh project a much smaller haul, about $30 billion, not $100 billion. They point to known changes in the taxpayer base and to likely moves that reduce what the state can collect. They also add a “litigation survival” discount to reflect legal risk. Their summary places expected proceeds between $28 billion and $36 billion, with $30 billion as a central estimate.

The Stanford analysis highlights the public exits of seven billionaires who left California after the proposal drew attention. Those departures remove about $540 billion from the potential tax base, or roughly 30% of total billionaire wealth tied to the state. Fewer resident billionaires also means fewer future capital gains and income-tax payments. That shrinkage is central to the lower revenue range critics present.

The Potential Net Loss to California’s Budget

Jaros and Rauh estimate that a smaller billionaire population would reduce annual state income-tax collections by about $1 billion to $3.5 billion going forward. When they compare the present value of those ongoing losses to the one-time wealth-tax proceeds, they find a negative result of about $39 billion. In plain terms, the state could end up worse off if departures persist and if the tax base continues to shrink.

Reason and other outlets report that a large share of plausible scenarios in the Stanford modeling produce a net loss. The message is simple and potent: you can tax paper wealth once, but you may lose steady income taxes for years if people move away. For many readers across the political spectrum, that risk echoes a core worry about government plans that look good on paper yet fail in practice.

Key Uncertainties: Valuation, Mobility, and the Courts

Both sides rely on models that hinge on sensitive assumptions. The Berkeley estimate assumes a 10% cut for avoidance and evasion, but that figure may be too low if more residents shift assets or leave. The Stanford estimate assumes that public exits reflect a broader trend. The true taxpayer count, the value of privately held assets, and how courts treat residency and retroactivity will affect the final number. Each of these adds uncertainty to what the state can actually collect.

Researchers at Stanford concluded that 85% of "plausible scenarios" from the California wealth tax proposal result in negative revenue for the state.

The question is if my former state of California will be stupid enough to pass it.

— Silicon Strategies (@siliconstrat) October 20, 2026

International evidence also shows that wealth taxes collect less than expected when design and behavior collide. Studies in Europe find that revenue depends on how the rules handle mobility, valuation, and compliance. Some countries raise modest sums; others drop the tax after weak results. That record does not decide California’s case, but it warns that design details and taxpayer response can overwhelm headline estimates if they are not realistic or enforceable.

What This Means for Voters and Taxpayers

Voters face a choice between a bold, one-time levy that promises a quick windfall and a risk that the ongoing tax base shrinks. Supporters say the plan targets a few hundred billionaires to fund vital programs during a federal pullback. Critics warn the policy could drain long-term revenue if more wealthy residents move or restructure their assets. The gap between $100 billion and $30 billion is not just a math fight; it is about who stays, who pays, and for how long.