- A sports event contract is a yes/no share that pays $1 if the outcome happens and $0 if not. Its price in cents is the market's implied probability, so a 62¢ contract says about 62%.
- A sportsbook builds its margin into the odds. A -110 line on both sides implies 52.38% each, 104.76% in total. An exchange-style market charges a fee on the trade instead.
- On Kalshi, 100 contracts at 50¢ cost $1.75 in taker fees, so the price you need the team to beat is 51.75%, against 52.38% for -110. Polymarket's sports rate gives 51.25%. These are our own hypothetical comparisons, not a quote from either platform.
- The fee gap is small next to the real question: whether your estimate of the game beats the price. Fees only decide how much edge you need.
Prediction market sports contracts work differently from a sportsbook bet in three ways: who takes the other side, where the house's cut shows up, and what you can do before the game ends. This page explains each with worked arithmetic from the published Kalshi and Polymarket fee formulas. It is not advice or a ranking of venues, and wallets and prices described here are aggregates as of the 2026-11-09 snapshot (method on our methodology page).
Prediction market sports contracts: what a sports event contract is
An event contract is a share in one outcome of an event. A moneyline market on a game, for instance, has a contract for each team. If your team wins, the contract settles at $1; if not, at $0. In between, it trades at any price from 1¢ to 99¢, and you can sell it before the game ends, so you do not have to hold to the final whistle.
The price reads as a probability. At 62¢ the market implies roughly a 62% chance, and the same arithmetic works for spreads, totals and season futures. Our guide to reading a 72-cent contract goes through it step by step, and this spread-market walkthrough shows a sports example.
Who is on the other side of your trade
At a sportsbook, the book sets the line and takes your bet. On an exchange-style venue, you trade against other participants through an order book: a list of waiting buy and sell orders. A taker accepts a posted price; a maker posts one and waits. The venue earns from fees rather than from the odds.
That structure explains why the two kinds of price look different. A sportsbook's two sides add up to more than 100%. An exchange's two sides, bought separately, add up to roughly 100% before fees.
Where the house margin shows up
Convert American odds to a probability and the sportsbook margin is visible. At -110 you risk $110 to win $100, so the implied probability is 110 ÷ 210 = 52.38%. With -110 on both sides of a spread, the two add up to 104.76%. The extra 4.76 points is the book's built-in margin, often called the vig or overround. A -200 and +170 moneyline pair works the same way: 66.67% plus 37.04% is 103.70%.
On a prediction market there is no built-in margin. The cost is the fee, which both venues publish as a formula. Kalshi's taker fee is round up(0.07 × contracts × price × (1 − price)), under its schedule effective 2026-07-07, and its default maker multiplier is 0. Polymarket charges takers contracts × rate × price × (1 − price), with a sports rate of 0.05, and makers pay nothing (fee documentation, see sources). Combo markets on Kalshi use a taker multiplier of 2, so a multi-leg contract costs more to take.
The arithmetic side by side
The table works the formulas for 100 contracts bought as a taker and adds the break-even probability: the price plus the fee per contract. This is our own calculation on the published formulas, computed 2026-11-09, and the sportsbook row is a standard -110 example rather than a quote from any book.
| Price | Kalshi fee | Kalshi break-even | Polymarket sports fee (0.05) | Polymarket break-even |
|---|---|---|---|---|
| 10¢ | $0.63 | 10.63% | $0.45 | 10.45% |
| 20¢ | $1.12 | 21.12% | $0.80 | 20.80% |
| 50¢ | $1.75 | 51.75% | $1.25 | 51.25% |
| 80¢ | $1.12 | 81.12% | $0.80 | 80.80% |
| 90¢ | $0.63 | 90.63% | $0.45 | 90.45% |
| Sportsbook -110, either side | Break-even 52.38%, built into the odds | |||
Two readings follow. For an even-money game, the exchange fee at 50¢ is lower than the -110 margin, which is why prediction markets are often described as cheaper. But the table also shows that the fee is a larger share of the stake on longshots: 0.63 on a $10 position at 10¢ is 6.3%. If you buy cheap sub-20¢ contracts as a taker, you pay the most relative to what you put up. The same shape is in our fees and break-even guide, and you can run your own price and size in the fee calculator.
What a sportsbook still does better
- Bet types. Same-game parlays, player props and in-play lines are deep at sportsbooks. Exchange-style venues list fewer of them, and a thin book can mean your fill differs from the quote.
- Familiar settlement. A sportsbook's house rules are one document; an event contract settles under the market's own rules text, which you should read before trading, including how a postponed or shortened game is handled.
- Promotions. Sportsbooks run bonuses and odds boosts; venue sign-up offers differ. Our DraftKings Predictions review covers one sportsbook's prediction product.
What the data says about who profits in sports markets
Our tracked leaderboards for Polymarket sports show how concentrated the winnings are. As of 2026-11-09, the all-time sports board lists 50 wallets with $242.1M in combined profit, and the top 10 hold 42.5% of it. On the last-month board the top 10 hold 53.1%. Wallets are not people, and a leaderboard shows winners, not the share of traders who lose. Even so, it argues against assuming a price is easy to beat. Our cohort study goes deeper.
Where this can go wrong
- Fee schedules change. The formulas above are as published at the snapshot date; the venue's current documentation governs.
- Kalshi rounds fees up per order, so very small orders pay proportionally more than the formula suggests.
- Availability differs by state, and the legal treatment of sports contracts is still being contested. See how Kalshi's legal battles with states affect what you can trade before planning around a venue.
- A lower fee is not an edge. If your probability is no better than the price, you lose the fee on every taker trade.
Frequently asked questions
Are sports prediction markets the same as sports betting?
They overlap in what you can trade on, but the mechanics differ. A sports event contract is a $1-or-$0 share traded with other participants, and the venue charges a fee. A sportsbook bet is placed against the book at odds that include its margin. Whether a given contract counts as betting under state law is contested.
Are sports prediction markets cheaper than sportsbooks?
Near even odds, the published taker fees work out lower than the 4.76-point margin built into a -110 line: 1.75¢ per contract on Kalshi at 50¢. On cheap longshots the fee is a bigger share of what you stake. Compare on the price you would actually trade.
What is a sports event contract?
A share in one outcome of a game or season. It settles at $1 if the outcome happens and $0 if not, and trades between 1¢ and 99¢ beforehand.
Can you sell a sports contract before the game ends?
Usually yes, if there are buyers at a price you accept. You can exit early at the then-current price, which may be better or worse than your entry. Thin books can make that exit costly.
Next steps
Browse live prices on the sports markets page, compare venues on the compare page, or start with what prediction markets are if the vocabulary is new.
The short version: a sportsbook shows its cut in the odds, an exchange shows it in a fee, and in both cases your own estimate has to beat the price plus the cost.