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.

How does a Kalshi price work?

A contract trades in cents, and the price is the implied probability. A Yes at 47 cents implies a 47% chance. The Yes and No prices sum to a few cents over 100, and that gap does the same job the vig does on a sportsbook line.

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 vig on 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.

What do Kalshi’s fees cost?

The fee depends on the price and on which schedule the series publishes. It peaks at a 50 cent contract and shrinks toward both extremes, and a resting order pays less than one that crosses the spread. Fairline reads the schedule Kalshi publishes for each series.

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.

What is a resting order, and what does it risk?

A resting order sits on the book at a price you pick and waits for someone to trade into it, instead of taking whatever is available now. It buys you a better price and costs you certainty. Two things can go wrong, and both are below.

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 is folded in.

A resting order carries two risks a taker does not run. It can execute after the market has already moved against its side, and an unfilled order returns nothing at all. Fairline prices Kalshi as one more book and leaves the order type to you.

What else separates an exchange from a sportsbook?

Who takes the other side, and what that party wants from you. Kalshi earns its fee on the trade whichever way the event settles, so a winning trader is no threat to it. A sportsbook is your counterparty, and it limits or bans bettors who win.

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.

Sources

• Kalshi's own API documentation, including the per-series fee schedule
• The public Kalshi exchange endpoint Fairline reads prices from