Kalshi vs Sportsbooks: How Event Contracts Price Sports

Kalshi is a regulated exchange where you trade event contracts against other users. A sportsbook quotes you its own price and takes the other side of the bet. The differences that matter for a bettor are the fee model, the order book, and who you are actually trading against.

Price discovery

Each contract trades in cents, and the price doubles as an implied probability. A Yes trading at 47 cents implies a 47% chance the event happens. Add the Yes and No prices together and the total lands a few cents over 100 rather than exactly 100, and that spread plays the same role as the vigon a sportsbook line. In Fairline’s own capture, Kalshi’s displayed two-way overround on MLB moneylines ran about 4.5%, in line with what the sportsbooks post. The low-vig pitch for prediction markets holds only inside tight, liquid windows.

The fee math

Kalshi publishes a fee type and multiplier for each series. Taker trades on a quadratic series use a fee based on 0.07 × P × (1 − P), scaled by that multiplier. A maker is a resting limit order that waits in the book instead of crossing the spread immediately. Series marked quadratic_with_maker_fees use a maker coefficient of 0.0175 × P × (1 − P), also scaled by the multiplier. Series marked quadratic currently apply no maker fee. Fairline reads the fee schedule published for that series and skips a market when the metadata is missing or unknown.

Resting orders

A resting order sits on the book at a price you choose and waits for someone to trade into it, instead of taking whatever price is available immediately. Resting a Yes at price x is a bet that the fair probability, call it p, sits above what you are paying once the current maker schedule and an adverse-selection buffer are folded in. The finder records a configured max from those inputs. It then shows one exact post based on the current best bid.

Fillability and adverse selection require forward evidence. A resting order can execute after the market moves against its side, and an unfilled order produces no return. Fairline records both outcomes before making an edge claim about these signals.

The other differences

A few other differences sit outside the price entirely. Kalshi is an exchange, so it earns its fee on the trade whichever side wins and has no reason to limit a profitable trader, while a sportsbook takes the other side of your bet directly and tends to limit or ban a bettor who wins consistently. Liquidity on many sports contracts is thin, with a wide gap between the best bid and ask, so a resting order can sit unfilled for a long stretch or fill at a worse average price than a book’s line would once size is factored in. Kalshi is a federally regulated exchange rather than a state-licensed sportsbook, and which states can trade its sports contracts has shifted as that status has been contested, so access is not guaranteed to stay the same from one month to the next.