Kalshi vs Polymarket arbitrage

Two exchanges, no sportsbook margin on either side, and two fee schedules that disagree about where trading is expensive. Kalshi charges a curve that peaks on near-even contracts; Polymarket charges a small flat fraction with a ceiling on it. A two-sided position between them is the one case on this site where the fee on BOTH legs has to be paid, and where ignoring either one changes the answer.

Two order books listing the same outcome will not hold the same price, because the people trading them are not the same people. Kalshi carries the wider menu of sports markets and the steadier participation; Polymarket concentrates its depth on whatever is being traded heavily that day. Where the two list the same bet, the gap that opens a position is a genuine difference of opinion between two crowds rather than a stale number.

Both legs are order books, so both legs can move under you — this is the only pair where neither side is a venue that must honour a posted price. Take the thinner book first. Beyond that, the two venues settle on different schedules and hold your capital for different lengths of time, and the two fees compound: a position whose posted prices imply a one percent margin can be flat once Kalshi's per-contract fee and Polymarket's taker fee are both paid.

Kalshi odds today. Kalshi charges a per-contract trading fee instead of building a margin into the line. The fee is a curve, not a flat rake: it peaks at roughly 1.75¢ on a contract priced near 50¢ and shrinks toward zero at both extremes, and maker fees are a quarter of taker fees.

Polymarket odds today. Polymarket's taker fee is a fraction of a percent, which makes its headline quote very close to the all-in cost and often the cheapest of the exchanges in the middle of the price range.

Leave this page open — the board above rescans itself as Kalshi's and Polymarket's prices move, so a position that opens while you're reading appears on its own rather than needing a reload. Right now the two are both quoting 2+ Touchdowns, 3+ Touchdowns, Anytime Touchdown, First Touchdown, Passing Touchdowns, Passing Yards, Receiving Yards, Receptions, Rushing Yards, Moneyline, Spread, and Total, which is the only ground a position between them can come from.

What a card here actually means

A fair line would put Kalshi's price and Polymarket's price on opposite sides of the same bet at exactly 100% of a certainty between them. This board only prints a card when the two real prices, net of both venues' fees, add up to less than that — the gap between 100% and what they actually sum to is the arbitrage, and the stake split tells you how to size each leg so both sides return the same amount whichever one wins. On a Kalshi vs Polymarket position that return is fixed rather than probable — expected value (EV) of a certain kind rather than a probable one, which is why it's usually smaller than a single-sided bet's edge.

Kalshi's leg is the one with a finite order book behind it on this Kalshi vs Polymarket pair — check its depth before you place the Polymarket side, since it's the side that can fill at a worse price or disappear while you're placing the second leg. Run Kalshi and Polymarket's exact numbers through the arbitrage calculator before you place either leg — the fee table above uses one fixed example, and your own prices won't match it exactly. For every other pair BeatVig tracks, see arbitrage bets today.