Legality in California
Both are CFTC-regulated and legal for California residents. Kalshi operates as a Designated Contract Market (DCM) directly. Polymarket is offering US event contracts through its acquired CFTC-licensed exchange. Kalshi has the longer regulatory track record; Polymarket was fined by the CFTC in 2022 before returning through acquisition.
Markets and coverage
Kalshi has the broadest US coverage today: politics, sports, economics, culture, weather, crypto. Polymarket's globally famous depth (especially political and cultural markets) hasn't fully migrated to its US product yet — initial US coverage skews toward sports. For broad market access in California right now, Kalshi wins.
Pricing & fees
Both charge modest per-contract fees competitive with traditional futures venues and dramatically lower than sportsbook vig. Kalshi's fees are transparently disclosed at order entry. Polymarket's US fee structure is still being finalized publicly. On liquid markets, real costs are comparable.
User experience
Kalshi's interface is finance-forward: clean, fast, category-organized, feels like a trading app. Polymarket's product has historically been more visual and social — prominent charts, news context, community commentary. Different audiences: Kalshi for execution focus, Polymarket for context-rich trading.
Who should use which
Use Kalshi if: you're opening your first California account, you want broad market coverage today, you value the longest CFTC track record. Use Polymarket if: you specifically want exposure to its global cultural and political markets as US coverage expands. Many serious traders will eventually hold both.
Want a second opinion? Read this outcome-driven head-to-head.