California is not yet chasing billionaires with a wealth tax, but it is preparing to. The main enforcement tool today is the Franchise Tax Board's residency audit, and voters will decide on a new one-time billionaire tax, Proposition 40, on November 3, 2026.
Proposition 40 is a proposed amendment to the state constitution. As the Legislative Analyst's Office explains, it would impose a one-time 5% tax on the net worth of anyone worth $1 billion or more. It is not law, and it needs voter approval to take effect.
Table of Contents
- What Proposition 40 would actually tax
- The dates that decide who pays
- How "enforcement" and "tracking" really work
- Why a move away may not help
- The measure could still lose in court
- Frequently Asked Questions
What Proposition 40 would actually tax
Prop 40 targets net worth, not income. Net worth is everything you own—stocks, real estate, business stakes—minus what you owe. The tax is a single 5% levy on that total, and it only applies once a person reaches the $1 billion mark. Married couples do not get two thresholds.
According to the California Budget & Policy Center, a couple is treated as one filer, so the $1 billion test applies to their combined wealth. The measure also reaches certain trusts, which are legal structures the wealthy often use to hold assets. For a celebrity or founder near the line, this matters. A stake in a private company or a large art collection counts toward the total, even though those assets produce no cash until sold.
The dates that decide who pays
Timing is the trap in Prop 40. The tax applies to people who were california residents on January 1, 2026. Net worth is then measured on December 31, 2026, and payment comes due in 2027. The LAO analysis makes the key point clear: this is a hard snapshot.
Someone who was a resident on that January date cannot escape the tax by moving away later in the year. There is no midyear proration that shrinks the bill for a partial-year resident. So the residency question is settled by a single day that has already passed. That design is deliberate, and it shifts the real fight to proving where someone truly lived.
How "enforcement" and "tracking" really work
There is no squad of agents seizing mansions. The enforcement mechanism is the residency audit, run by the Franchise tax Board, California's income-tax agency. As Kugelman Law describes, these audits test whether a departing taxpayer genuinely cut ties to the state. Auditors weigh where your home, family, and professional and social life are based, plus how many days you spent in California.
To count those days, they can reach for hard data. Industry reporting notes that cell-phone and GPS location records, plus the locations of card transactions, can all become evidence of days spent outside the state. That is what "tracking methods" means here—reconstructing a calendar from digital trails, not surveillance in real time. A person who claims to have left but keeps a home, doctors, and dinner reservations in Los Angeles has a weak case.
Why a move away may not help
California has no standalone "exit tax." A Berkeley expert analysis confirms there is no departure levy; the pressure on people who leave runs through existing residency-audit law instead. For Prop 40 specifically, the January 1, 2026 snapshot means leaving now does not undo a resident's liability for the one-time tax.
Going forward, a genuine move can change future obligations, but only if the ties are truly severed and can be documented. A few practical realities for anyone weighing a departure:.
- The burden falls on you to show the move was real, not on the state to disprove it.
- Keeping a California home, business role, or family base undercuts a claim of non-residency.
- Day counts matter, and your phone and payment records may tell a different story than you do.
The measure could still lose in court
Passing at the ballot box would not settle the matter. The measure faces serious legal challenges, and a court could strike it down. California Globe reports that Prop 40 may be attacked under the U.S.
Constitution—on grounds including the dormant Commerce Clause, due process, equal protection, and the ban on bills of attainder—as well as under the California Constitution's limits on ad valorem taxes and its education-funding rules. Voter approval is a start, not a guarantee of survival. The revenue math also carries a warning for the state itself. The LAO estimates California "probably would collect tens of billions of dollars" over several years, yet projects an ongoing loss of hundreds of millions a year if wealthy residents leave.
Frequently Asked Questions
Is Proposition 40 the law right now?
No. It is a proposed constitutional amendment on the November 3, 2026 ballot and needs voter approval before it can take effect.
Does moving out of California avoid the Prop 40 tax?
Not for the one-time tax. It applies to anyone who was a resident on January 1, 2026, and leaving afterward does not remove that liability.
Can auditors really use my phone location?
Yes. Residency audits can draw on cell-phone and GPS records and card-transaction locations to count the days you spent inside or outside California.