Prediction Market Arbitrage

Prediction market arbitrage occurs when a trader buys and sells contracts on the same outcome at prices that, taken together, secure a profit regardless of how the event resolves. The pattern appears in two main forms. Cross-venue arbitrage exploits price differences for the same outcome listed on two exchanges, for example a contract trading higher on Kalshi than on Polymarket. Intra-market arbitrage exploits situations within a single prediction market where the Yes price and the No price of binary outcome shares sum to more or less than one dollar, leaving a riskless spread for whoever trades both legs.

Arbitrage activity is a stabilizing force rather than a drain on a venue. As arbitrageurs buy the underpriced side and sell the overpriced side, they push quotes back toward a consistent implied probability, which tightens spreads and improves prediction market liquidity for everyone trading on the central limit order book. The presence of active arbitrageurs is therefore a signal of a healthy, efficiently priced market, and their absence often points to thin or stale order books that need market-making support.

Real-world arbitrage is constrained by friction. Trading fees, the bid-ask spread, slippage on larger orders, settlement timing differences between venues, and the capital locked up until market resolution all narrow or erase a theoretical edge. A gap that looks profitable on screen frequently disappears once execution costs are netted out, which is why durable price discrepancies are rare on liquid contracts and most common on newly listed or low-volume events.

For operators and affiliates, prediction market arbitrage differs from generic arbitrage betting across sportsbooks because the counterparty is the open market, not a house line that an operator can limit or void. Operators reading their books can treat consistent arbitrage volume as evidence that their prices are competitive, while affiliates assessing a venue can use spread tightness and the speed at which mispricings close as a proxy for execution quality before directing traffic to a prediction markets product.