A sports bet is a contract with a bookmaker, who sets the odds with a built-in margin and takes the other side; a prediction market lets traders buy and sell outcome shares with each other at a public price, with a trading fee instead of a margin and the option to sell before the end. In the US the difference is also legal: sportsbooks are licensed by states, while prediction markets on sport are listed by federally regulated exchanges, which several states are contesting in court. Nimb shows sports markets on its map but does not index same-day fixtures.
How do prediction markets and sportsbooks compare?
| Prediction market (Polymarket, Kalshi) | Sportsbook | |
|---|---|---|
| Counterparty | Other traders | The bookmaker |
| Price | Set by the order book, from $0.01 to $0.99 | Odds set by the book |
| Cost | Spread plus a taker fee (Polymarket sports: 0.05 × p × (1 − p) per share) | Margin built into the odds, often several percent across both sides |
| Exit early | Sell at the market price | Cash-out at the book's price, if offered |
| Winning accounts | Not limited for winning | Can be limited |
| Bet types | Mostly winner, spread and totals; fewer props | Wide range of props and parlays |
| US regulation | CFTC (federal); contested by some states | State gaming regulators |
| Promotions | Few | Bonuses, boosts |
How do you convert sports odds to a prediction market price?
Decimal odds of 2.50 imply 1 ÷ 2.50 = 40%; American odds of +150 also imply 40%, and −150 imply 60%. A prediction market price of $0.40 is the same 40%. Bookmaker odds on both sides add up to more than 100% (the margin), so remove it before comparing: if Team A is 1.80 (55.6%) and Team B 2.10 (47.6%), the total is 103.2%, and the fair chances are about 54% and 46%. Polymarket odds explained.
Is a prediction market cheaper than a sportsbook?
Often, on liquid games: a 1-point spread plus Polymarket's sports taker fee (at 50%, 0.05 × 0.5 × 0.5 = $0.0125 per share, 2.5% of the price) can cost less than a bookmaker's margin. On thin markets a wide spread can cost more. Compare the all-in break-even, not the headline odds. Fees and all-in pricing · Spread and depth.
Is it legal?
Depends on your country and, in the US, your state. In 2026 federal appeals courts split on whether states can apply gambling laws to sports event contracts. Polymarket's international platform does not let users in the US, UK, France and about 35 other countries open positions. Are prediction markets legal?
What does Nimb do with sports?
Sports markets appear on the map in khaki, with the same reading and ticket, but most are single fixtures that settle within hours, so Nimb keeps them out of search indexes and its movers list. Nimb does not offer tips or picks. Sports markets on the map · Are prediction markets gambling?
Frequently asked questions
Is Polymarket a sportsbook?
No. It is a peer-to-peer market with an order book; it does not set odds or take the other side.
Can you bet on sports with prediction markets?
Many prediction markets list sports outcomes. Whether you may trade them depends on your location.
Polymarket vs DraftKings predictions: what is the difference?
DraftKings is a US sportsbook that has also launched prediction products under federal rules; Polymarket's international platform is a crypto order-book market closed to US users, and Polymarket US is a separate CFTC-regulated exchange.
Last reviewed 8 November 2026 · Data from Polymarket · Not financial advice · Nimb is not affiliated with Polymarket.