Prediction Market Arbitrage Explained

Arbitrage is buying the same thing for less on one platform and selling it for more on another. In prediction markets, this happens when Polymarket prices an event at 60 cents YES while Kalshi prices the same event at 55 cents YES.

You buy YES on Kalshi at 55 and sell YES on Polymarket at 60. Regardless of the outcome, your net cost is negative — meaning you profit no matter what happens. This is textbook risk-free return.

Different platforms have different participant pools with different information and different biases. Polymarket leans crypto-native. Kalshi leans TradFi. These populations can genuinely disagree about probabilities, creating price gaps.

Arbitrage opportunities also arise from liquidity differences, platform-specific fee structures, and temporal delays in information propagation. They're not permanent — they get closed as arb traders exploit them — but new ones appear constantly.

Capital lockup is the biggest issue. Both legs of the arb tie up capital until resolution. If a market resolves in 6 months, your capital is locked for 6 months earning a 5-point arb. That might not beat simply trading with that capital.

Execution risk is real too. By the time you execute the second leg, the price might have moved. You need to be fast, or use tools that can execute both legs simultaneously.

Manual arb scanning is tedious. The best approach is automated monitoring that alerts you when price gaps exceed your threshold. Some traders build custom bots for this.

The gap has to be wide enough to cover fees on both platforms plus your opportunity cost of capital. For most traders, that means looking for 5+ point arbs with resolution dates within 3 months.

For most retail traders, pure arbitrage is too capital-intensive and too thin-margined to be a primary strategy. It's better as a supplement — a way to capture risk-free basis points while your capital would otherwise be idle.

Where arb thinking really helps is in identifying when one platform is mispriced relative to another. Even if you don't execute both legs, knowing that Kalshi and Polymarket disagree by 10 points tells you one of them is wrong. Figure out which one, and you have a directional trade.