A Polymarket-Kalshi price comparison becomes a potential arbitrage only after the contracts, order sizes and settlement conditions match. PredictPedia can help discover related markets, but a grouped event is not a certification that every contract has identical rules.

Step 1: Match the exact question

Open both provider pages. Copy the complete rule text and outcome identifier, then compare the source and deadline. Kalshi publishes a market rules summary; Polymarket distinguishes the question title from the conditions used for resolution.[1][2]

For an election, check whether each contract covers nomination, election victory or taking office. For economic data, compare the release, series, adjustment method, threshold and treatment of revisions. Record any difference before looking at a profitable price.

Step 2: Obtain both executable offers

Choose the Yes side on one venue and the No side on the other. On a Kalshi binary book, the opposing bid determines the complementary ask, as documented by its API.[5] Confirm the available offer in the trading interface rather than using a chart mark or an old last trade.

Work in dollars per contract on both sides. A value written as 42 cents is $0.42, not $42. Ensure each contract has the assumed $1 payout and that quantities refer to the same number of outcomes.

Step 3: Include current fees

Read Polymarket's market-specific fee parameters and Kalshi's current schedule, then check the actual order previews.[3][4] Neither a remembered percentage nor a generic claim that a platform is free is sufficient.

For a hypothetical 80-pair trade, Yes costs $0.43 and No costs $0.54. Entry cost is $77.60 before fees. If the two previews together add $1.60, total cost becomes $79.20 against a normal paired payout of $80. The remaining margin is only $0.80. A one-cent deterioration on each of 80 contracts on either side would consume that margin.

Step 4: Plan an incomplete fill

Write a maximum cost and quantity for each order. Keep enough accessible balance on both venues before execution; transferring money after the first fill creates delay. Check which side filled and cancel any unwanted remainder.

If 80 Yes contracts fill but only 50 No contracts do, you hold 50 pairs plus 30 unhedged Yes contracts. Calculate that residual exposure separately. Do not report the entire trade as arbitrage profit.

Step 5: Follow both settlements

Track each contract until settlement and withdrawal are complete. An outcome visible in the news does not mean both accounts have paid. Save rules, fills, fees and the final payout for review. The general arbitrage guide explains the payoff table and return calculation in more detail.

References

Kalshi Help Center. Market Rules. March 17, 2026; accessed October 13, 2026.
Polymarket Documentation. Resolution. Accessed October 13, 2026.
Polymarket Documentation. Fees. Accessed October 13, 2026.
Kalshi. Fee Schedule. Current schedule linked by the exchange; accessed October 13, 2026.
Kalshi API Documentation. Orderbook Responses. Accessed October 13, 2026.

Arbitrage Across Polymarket and Kalshi