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Sports prediction markets vs. sportsbooks.
Short answer
A sportsbook sets odds and builds its margin into them. A sports prediction market lets traders set the price, and the platform charges a fee. To compare them, remove the sportsbook’s margin and add the market’s fee and spread, then compare probabilities.
What a sports prediction market is
A sports prediction market lists event contracts on games: “Will the Eagles beat the Cowboys?” settles at $1 if they do and $0 if they do not. Kalshi lists sports contracts on its CFTC-regulated exchange, Polymarket lists them on its own venues, and Robinhood began offering sports event contracts through Kalshi in 2025 (Axios). Which markets you can access depends on the platform and your state.
Who sets the price
| Sportsbook | Prediction market | |
|---|---|---|
| Price set by | The book’s traders | Other traders’ orders |
| How it earns | Margin (vig) built into odds | Trading fee per contract |
| Your counterparty | The sportsbook | Another trader, via the exchange |
| Price format | American or decimal odds | Cents per $1 contract |
| Exit before the game ends | Cash-out offer, if any | Sell at the current bid |
| Limits on winners | Books may limit accounts | Limited by market depth |
The practical consequence: a sportsbook price includes the book’s margin and its view of risk; an exchange price reflects whoever is willing to trade at that level, plus a separate fee. Neither is automatically cheaper.
Step 1: turn a moneyline into a fair probability
Say a book offers Team A at −150 and Team B at +130.
- Negative odds: odds ÷ (odds + 100). 150 ÷ 250 = 60.0%.
- Positive odds: 100 ÷ (odds + 100). 100 ÷ 230 = 43.5%.
Those add to 103.5%. The extra 3.5% is the vig. Divide each by the total to remove it: Team A’s no-vig probability is 58.0% and Team B’s is 42.0%. This is the book’s implied fair line.
Step 2: turn a contract price into a real cost
Now suppose the exchange shows Team A Yes with a 57-cent ask. At Kalshi’s general 0.07 taker rate, 100 contracts cost $1.72 in fees, or 1.72 cents each (fee tables). Your all-in cost is 58.7 cents, which is a break-even probability of 58.7%, roughly −142 in American odds.
Step 3: compare like with like
| Source | Break-even probability | Equivalent odds |
|---|---|---|
| Sportsbook at −150 | 60.0% | −150 |
| Exchange at 57¢ + fee | 58.7% | ≈ −142 |
| No-vig fair line | 58.0% | ≈ −138 |
In this example the exchange is the cheaper way to back Team A, but neither price is below the no-vig fair line, so neither is a clear value bet on that evidence alone. You would need a reason, such as a model or news, to believe Team A’s true chance is above 58.7%.
Before trusting any comparison, check that the outcome definitions match: moneyline versus regulation-only, overtime, postponements and how each venue settles voided games.
Where an independent model comes in
Book and market prices are both opinions. A third, independent estimate lets you see when they might both be off. Kelix Lines simulates each matchup 10,000 times from opponent-adjusted ratings and shows the model’s probability beside available Kalshi, Polymarket and sportsbook prices, with timestamps. Browse upcoming game comparisons or read the model methodology.
A model disagreeing with the market is a research lead, not a guaranteed edge. See how to measure who was right over many games.
Are sports prediction markets legal?
That question is being litigated. Several states argue sports event contracts are gambling under state law; exchanges and the CFTC argue federal law governs. Appeals courts reached different conclusions in 2026. Our regulation explainer summarizes where things stand.
Frequently asked questions
Are sports prediction markets the same as sports betting?
Economically they look similar to the person placing the trade. Structurally they differ: an exchange matches traders and charges a fee, while a sportsbook takes the other side. Whether states may regulate them as gambling is being decided in court.
How do I convert a moneyline to a probability?
For negative odds, divide the odds by the odds plus 100 (−150 → 150 / 250 = 60%). For positive odds, divide 100 by the odds plus 100 (+130 → 100 / 230 = 43.5%). Then remove the vig by dividing each by their sum.
Does Robinhood have sports prediction markets?
Robinhood began offering event contracts through Kalshi in 2025. Market availability changes by product and state, so check the app directly for current listings.
Which is cheaper, a sportsbook or an exchange?
It varies by game and time. Compare the no-vig sportsbook probability with the exchange’s ask plus its fee for the same outcome and settlement rules.
Educational content, not financial, legal or tax advice. Prediction markets involve risk, including loss of capital. Examples are illustrative calculations, not live quotes or trading results. Kelix is independent of Kalshi, Polymarket, Robinhood and sportsbooks.