How to Find Arbitrage Opportunities on Polymarket and Kalshi

A prediction-market arbitrage candidate appears when equivalent outcomes trade at different prices across venues. The common pattern is buying Yes on the cheaper venue and No on the other venue when the combined cost is less than the payout.

The word candidate matters. A visible gap is only useful after fees, liquidity, timing, and contract wording all still make the trade work.

Start with markets that are already matched across Polymarket and Kalshi. This removes most of the tab switching and lets you focus on whether the spread is real.

1. Open the arbitrage page or search for a specific event.
2. Filter to markets available on more than one exchange.
3. Sort by the largest fee-adjusted gap.
4. Ignore anything where one side is stale, closed, or thin.

Use fee-adjusted prices, not headline prices. If Yes on one venue plus No on the other costs less than the payout, the difference is the gross spread before execution risk.

• Compare the side you would actually buy, usually Yes on the cheaper venue and No on the other.
• Use the fee-adjusted cost shown by LocksBet when available.
• Check that the spread is large enough to survive slippage.
• Treat tiny gaps as research leads, not automatic trades.

Similar titles are not enough. Before acting, open both venue pages and confirm that the markets resolve on the same event, timeframe, and source of truth.

• Do both contracts use the same resolution criteria?
• Do close dates and settlement timing line up?
• Are edge cases handled the same way?
• Is the market still open and active on both venues?

The final check happens on the exchanges. Prices can move, displayed size can be small, and one leg can fill while the other does not.

1. Refresh both venue pages.
2. Confirm available size at the prices you plan to take.
3. Account for fees and any expected slippage.
4. Use smaller size when a market is thin or moving quickly.
5. Keep a record of the contract wording and execution prices.