After-fee price gaps: Kalshi vs Polymarket

The matched-outcome set comes from a manual review queue: a pair is included only after a human confirms that two markets — one on Kalshi and one on Polymarket — resolve to the same outcome. We use the Yes ask price from each side (the cost to enter a long Yes position) and add the exchange’s fee for that price level to get an after-fee per-contract cost.

Kalshi’s fee is computed from its standard taker schedule (and the lower INX/NASDAQ schedule for those tickers). Polymarket fees are computed only for fee-enabled markets and use the per-token fee rate when available. The signed gap is polymarket_after_fee − kalshi_after_fee, in cents — positive means Kalshi is cheaper.

We drop pairs without a current Yes ask on both sides, and require a current Yes bid plus a bid-ask spread of 10¢ or less on each venue so thin books don’t dominate the analysis. Outliers beyond the 2nd–98th percentile are clamped to the histogram’s end bins so they don’t squash the rest of the distribution.

Categories assigned by exchange are unified by preferring the more specific tag if either side is “other”. Why LocksBet exists →