Per side: kalshi 0.07 x P x (1-P) per side (max 1.75c at 50c) (published), polymarket 1000 bps x min(P, 1-P) per side (max 5.00c at 50c); rate assumed, varies by market (published), opinion 0.04 x P x (1-P) per side (max 1.00c at 50c), taker only; excludes its $0.25 minimum fee (published), limitless 0.75c per side (flat), unknown venues 7.50c per side.

published= the formula is verified from the venue itself — not that every input is known. Polymarket's fee is per-market and the rate used is a conservative default, so a market that charges nothing is overstated. Unmarked venues are unverified estimates end to end.

Net edge subtracts both legs' costs and excludes resolution or structure mismatches. Prices are ingest snapshots, not live quotes; stale rows are flagged and never marked actionable.