California's proposed billionaire tax would raise substantial public revenue without causing enough economic harm to outweigh its benefits

What's this about?

People disagree about whether California’s planned tax on billionaires would help the state more than it hurts.

The plan would take a one-time share of their total wealth, not just their yearly pay.

What supporters say

• The tax could bring in about $100 billion from 2027 through 2031, giving the state much more money for public needs.
• The tax could reach wealth from rising share and business values, which normal income taxes often miss.
• Taxing huge fortunes could make wealth and chances more fairly shared across families.

What critics say

• Some rich people might leave California, which could cut future tax money and erase the planned gain.
• The tax could lead to less investing, fewer jobs, and less business growth in the state.
• Hard-to-value assets and efforts to avoid the tax could make the state collect much less money.

How to read this

The number of points on each side does not show who is right; the strength of each point’s proof matters more.

The bottom line

The tax could raise a very large sum, but that amount is only a guess based on many uncertain facts.

We are not sure yet whether its gains would beat losses from people leaving, less growth, and tax avoidance.

California’s proposed one-time tax on billionaire wealth could raise a large sum for the state. But the central question is whether that money would outweigh possible losses from migration, tax avoidance, weaker investment and the cost of administering the plan.

The case for

The strongest argument is fiscal. One expert estimate puts the tax’s revenue at about $100 billion from 2027 through 2031, or roughly $20 billion a year. That would be a significant amount compared with California’s $251.5 billion General Fund spending plan for 2026–27. The estimate depends on assumptions about wealth, residency, compliance and asset values, however, so it shows the tax’s potential rather than a guaranteed result. 1 (see Figure 2)

Supporters also argue that the measure would reach wealth that regular income taxes often miss. Much of a billionaire’s wealth comes from rising values in businesses and shares—gains that may not be taxed until assets are sold, if they are taxed at all. One analysis estimates that California billionaires paid about $3 billion a year in state income taxes from 2019 through 2025, while arguing that their tax burden was low compared with their economic gains. 2

A further argument is fairness. Taxing concentrated wealth could raise money from people who have benefited from large inherited or accumulated fortunes and could reduce advantages linked to family resources. Research from Norway has connected parental wealth and wealth taxation to the distribution of opportunity. But those findings do not directly measure how California’s proposed tax would affect equality. 3

The case against

The most serious challenge is that wealthy residents could leave or reduce their California tax presence, cutting future income-tax collections. An NBER analysis estimates that California billionaires currently provide between $3.3 billion and $5.8 billion in annual state income-tax revenue. Under its assumptions, departures could produce a $38.9 billion loss in net present value, potentially offsetting much of the new tax revenue. 4 (see Figure 1)

Other research supports the idea that high earners respond to differences in state taxes by changing reported income or residence. Scandinavian evidence also links higher wealth-tax exposure to increased migration and measurable economic effects. Those studies point to a real risk, but they do not show exactly how many people would leave under California’s one-time proposal. 4 (see Figure 3)

The tax could also collect less than expected because billionaire assets are difficult to value. Private companies, trusts, artwork and other holdings can be hard to price, creating opportunities for disputes and avoidance. Research on wealthy taxpayers documents substantial evasion, while European experience suggests that wealth taxes often raise less than expected because of avoidance, administrative costs and wealthy-person outflows. 5

Economic effects could extend beyond tax compliance. Relocation or forced asset sales might reduce investment, entrepreneurship and related income-tax revenue. Studies provide evidence that migration can have broader economic consequences, but there is no reliable estimate of the size of those effects for this specific one-time California tax. 6

The bottom line

The evidence supports the claim that California’s tax could raise substantial gross revenue, but it does not show with similar confidence that the tax’s overall benefits would exceed its fiscal and economic costs. Supporters project about $100 billion in receipts, while the NBER analysis projects a $38.9 billion negative net present value after migration-related income-tax losses; the estimates use different assumptions about residence, compliance, valuation and how long lost tax payments would continue.

Overall, the evidence leans against treating the proposal’s net benefits as established. Confidence is moderate, not high: the revenue opportunity and the risk of taxpayer response are both credible, but migration, avoidance, valuation problems and enforcement costs leave the final outcome unresolved.