Cross-platform arbitrage exists when the same real-world event is priced differently on two prediction markets. Buy on the cheaper venue, sell on the more expensive one, lock the spread regardless of outcome. All spreads below are net of estimated platform fees (~2% Polymarket taker, ~1.5% Kalshi). Run your own numbers →

How cross-platform arbitrage works

What is a "bps" spread?

One basis point equals 0.01¢ per contract. A 100 bps spread means you lock 1¢ of profit on every $1 pair you trade, after fees. Bigger spread, bigger edge.

How is ROI calculated?

ROI is net profit divided by total capital deployed (cost of the YES leg plus the NO leg of the hedge). It is the return on the money you actually lock up, not on contract notional.

What does "direction" mean?

"BUY K → SELL P" means buy the YES contract on Kalshi and sell YES on Polymarket (or equivalently buy NO on Polymarket). The opposite direction is the inverse pair.

Why do spreads exist?

Polymarket and Kalshi serve different user bases, settle differently, and update at different speeds. The price gap is the cost of that friction. Scanners surface it; execution is on you.