01.What Is Polymarket Arbitrage?
Arbitrage is the practice of exploiting price differences to lock in a profit regardless of outcome. On Polymarket, two types of arbitrage are most common.
- Multi-outcome arbitrage: when the probabilities of all outcomes in a single market sum to less than 100%, you can buy all outcomes and guarantee a profit (also called a "dutch book").
- Cross-platform arbitrage: when Polymarket and another prediction market (Kalshi, Metaculus, Manifold) price the same event differently, you can buy the underpriced side on one and sell (or hedge) on the other.
02.Multi-Outcome Arbitrage Explained
Suppose a binary market has YES trading at 48¢ and NO trading at 49¢. The sum is 97¢ — less than $1. If you buy $0.48 of YES and $0.49 of NO ($0.97 total), you receive $1.00 regardless of outcome. That is a guaranteed $0.03 return on $0.97 invested (~3.1%).
- Works best in binary and low-liquidity markets where spreads are wider.
- Profits are small per trade — volume and automation are key to making it worthwhile.
- Risk: execution slippage if market moves while you are placing both legs.
- Tools: parlay calculators and arb scanners automate the math across many markets simultaneously.
03.Cross-Platform Arbitrage
Cross-platform arb requires the same event to be listed on multiple prediction market platforms at different prices. You buy the underpriced side on one platform and the opposite (or a hedge) on another.
- Requires accounts and capital on multiple platforms (Polymarket, Kalshi, etc.).
- Spreads are usually small — meaningful only with significant capital or frequent trades.
- Aggregator tools compare prices across platforms in real time.
- Settlement differences (one market resolves before another) add complexity.
04.Tools That Help
Several tools are built specifically for Polymarket arbitrage. These automate scanning, calculation, and sometimes execution.
- Arb scanners: continuously monitor markets for sub-100% probability sums.
- Cross-market aggregators: compare Polymarket prices to Kalshi, Metaculus, and others.
- Parlay calculators: compute guaranteed profit scenarios for multi-outcome markets.
- Trading bots with arb strategies: automated execution once an opportunity is detected.
05.Risks and Practical Considerations
Arbitrage on Polymarket is not entirely risk-free. Understanding the practical challenges is essential before committing capital.
- Slippage: large orders can move the price before both legs are filled, eliminating the opportunity.
- Liquidity: many Polymarket markets have thin order books — not enough shares to fill meaningful arb trades.
- Gas and fees: on-chain transactions incur gas costs that eat into small profit margins.
- Resolution risk: markets can resolve in unexpected ways, especially for ambiguous events.
- Timing: cross-platform arb requires both positions to be live simultaneously.