Paste in any two prices and see the margin built into them — then what the identical bet costs on a prediction market, taking the price versus posting your own.
Enter both sides of a market. Both prices are needed: the margin only shows up when you add them together.
Assumes a one-cent spread on the prediction market, which is what liquid NFL and MLB games have run at. Fees: Polymarket US 0.0695 × price × (1 − price) per share, international 0.05. A limit order pays no taker fee — but it only saves you anything if it fills.
Cost of one bet on each side of 20 NFL and MLB games, priced 23 September 2026. Median: sportsbook 4.1%, Polymarket US market order 4.2%, international 3.3%.
| League | Game | Sportsbook | PM market | PM limit |
|---|---|---|---|---|
| MLB | MIN at SF | 4.47% | 4.21% | ~0% |
| MLB | MIL at PHI | 4.43% | 4.04% | ~0% |
| MLB | TOR at BAL | 4.41% | 4.37% | ~0% |
| MLB | WSH at DET | 4.41% | 4.31% | ~0% |
| NFL | MIN at TB | 4.35% | 4.26% | ~0% |
| MLB | TB at NYY | 4.33% | 4.92% | ~0% |
| NFL | ATL at GB | 4.17% | 3.62% | ~0% |
| NFL | HOU at IND | 4.14% | 4.22% | ~0% |
| NFL | PHI at CHI | 4.14% | 3.57% | ~0% |
| NFL | NYJ at DET | 4.12% | 4.19% | ~0% |
| NFL | SEA at WAS | 4.11% | 1.37% | ~0% |
| NFL | KC at MIA | 4.11% | 7.19% | ~0% |
| NFL | BAL at DAL | 4.11% | 3.92% | ~0% |
| NFL | LV at NO | 4.11% | 4.66% | ~0% |
| NFL | NE at JAX | 4.09% | 3.88% | ~0% |
| NFL | MIA at MIN | 4.06% | 9.26% | ~0% |
| NFL | CIN at PIT | 4.04% | 4.13% | ~0% |
| NFL | ARI at SF | 4.01% | 6.33% | ~0% |
| NFL | TEN at NYG | 4.01% | 3.97% | ~0% |
| NFL | LA at DEN | 3.97% | 4.26% | ~0% |
Odds are a price, and the price has a margin in it. Add both sides of a -110 line together and you get 104.76% rather than 100% — that extra 4.76% is the book’s cut, and it comes out whether you win or lose.
A prediction market works differently. You aren’t betting against a house, you’re trading with other people, and there are two ways to do it. Take a price someone else has posted and you pay a taker fee. Post your own price and wait for someone to meet it, and you pay nothing.
That second option is the whole story. On a coin-flip game a market order on Polymarket US costs roughly what a sportsbook does once the fee is counted. The saving isn’t in the venue — it’s in the order type.
The catch: a limit order only saves you money if it fills. Post a price in the middle of the spread and the market can move away while you wait. Cheap and certain don’t come together.