California's billionaire tax leaves a ten-month residency gap

California's proposed billionaire tax carries a quirk: the residency snapshot predates the tax's own enactment by ten months. The snapshot date is January 1, 2026. A Tax Foundation analysis, published in the San Diego Union-Tribune, calls the gap a planning opportunity. The November ballot measure would impose a one-time 5 percent tax on the net worth of billionaires who were California residents on that date. Their wealth would be measured on December 31.

The analysis opens with Mark Zuckerberg's February purchase of a Florida mansion. Because the law cannot take effect until early November, the reasoning goes, a billionaire who leaves California later this year could plausibly escape the tax, or part of it, even if the measure survives broader constitutional challenges. The Tax Foundation argues the residency language is vulnerable to legal challenge.

For advisors, this is a nudge to start the domicile review. The questions are practical: where the client actually lives, what steps would establish a new domicile, and what evidence — property, license, voter registration, days in state — would support a change before the snapshot date. The analysis suggests a credible move before year-end could be enough; it does not promise a guarantee.

The uncertainty cuts both ways. A client who relocates on the strength of the Tax Foundation's reading could still face a challenge from the state, and the legal fight could outlast the tax itself. The advisor's job is to put the calendar, the costs, and the odds on the table, and to make sure the client understands what is being bet.