Kalshi Fees Explained: How Contract Pricing and Trading Costs Work

Kalshi publishes an explicit trading fee formula rather than a flat percentage: the fee is calculated as 0.07 multiplied by the number of contracts, multiplied by the price, multiplied by one minus the price, rounded up. That formula isn't arbitrary, it's built around the statistical variance of a contract at a given price, and its practical effect is a fee that peaks when a contract trades near 50 cents and shrinks as the price moves toward either extreme.

Working through what that curve actually means in practice: a contract trading right at the middle of its range, where the outcome is genuinely uncertain, carries the highest fee per contract under this formula, since price times one-minus-price is maximized exactly at 0.5. A contract trading near 5 cents or 95 cents, where the market has already priced in a fairly confident outcome, carries a meaningfully smaller fee under the same formula, because that price-times-remaining-probability term shrinks sharply toward either end of the range.

That structure is a deliberate design choice, not an accident. A contract near the extremes carries less genuine two-sided trading risk for the exchange to price around, since the outcome is already close to settled in the market's own estimation, while a coin-flip contract represents the most genuinely contested, highest-uncertainty trade on the platform. Charging proportionally more for the higher-uncertainty trade and less for the near-certain one tracks the actual risk being taken more closely than a flat percentage-of-notional fee would.

This is also the direct opposite shape from Limitless Exchange's documented fee curve, which rises toward the extremes and tapers in the middle, worth knowing if you're comparing costs across platforms rather than assuming every prediction market prices risk the same way. Polymarket's documented common case, by contrast, is a $0 fee on most of its core markets regardless of where the price sits, which makes it the cheapest of the three for a trade near 50 cents specifically, where Kalshi's formula-based fee is at its highest.

The practical implication for a Kalshi trader is that cost isn't a fixed, predictable percentage the way it would be on a flat-fee platform, it depends on exactly where a contract is trading at the moment of the trade. A position taken early, while an outcome is still genuinely uncertain and priced near the middle of the range, costs more per contract under this formula than the same position taken later, once the market has moved toward a more confident price, which is worth factoring into the real, all-in cost of a trade rather than assuming Kalshi's published rate applies uniformly everywhere.