Proposition 42, a November 2026 California constitutional amendment, would bar new state taxes on personal property ownership such as retirement accounts, investments, and business interests while limiting retroactive levies tied to pre-enactment residency or conduct. The measure emerged as a direct counter to Proposition 40’s proposed one-time 5% wealth tax on billionaires, which relies on a January 1, 2026 residency snapshot and valuation date. Trader sentiment remains closely balanced near 52% against passage because the proposition pits broad anti-retroactivity protections and personal-asset safeguards against competing voter priorities on revenue for public programs. Recent signature qualification and early positioning of both initiatives on the same ballot have heightened attention to how overlapping tax-limitation language could affect outcomes. Upcoming campaign spending, endorsements from business groups or taxpayer organizations, and any legal challenges to Prop 40’s retroactive provisions could shift probabilities in either direction before November.