The short answer
A sportsbook takes its fee inside the odds. That fee is called the margin. Polymarket charges a visible fee when you buy instantly, and an instant buyer also pays the gap between the buy price and the sell price. Which of the two costs you more depends on the price of the bet, and on whether you buy instantly or with a limit order that waits for its price.
There is no single answer for every bet. On a 50/50 game, an instant buy on Polymarket can need about the same share of wins to break even as a standard −110 bet. At 20¢ it can need more, and at 80¢ it can need less. The math is below, step by step.
This page is about polymarket.com. Polymarket US has its own rules and is not covered here.
Where a sportsbook hides its fee
Take a game with two sides, both priced −110 (1.909 in decimal odds). Each price stands for a chance of winning: 1 ÷ 1.909 = 52.38%. Add the two sides and you get 104.76%, but the real chances of the two sides add up to 100%. The extra 4.76% is the book's margin. Bettors call it the vig or the juice; books call it the hold.
Say one person bets $110 on each side. The book takes $220. The winner gets $210 back: the $110 stake plus $100 profit. The book keeps $10, which is 4.55% of all the money bet (1 − 1 ÷ 1.0476 = 4.55%). No line on your bet slip shows this fee. You pay it as lower odds, whether you win or lose.
The margin is not the same on every bet:
- Big games at low-margin books. At −105 on both sides, each side stands for 51.22%. The total is 102.44%, and the margin is 2.38%.
- Side markets priced −120 on both sides. Each side stands for 54.55%. The total is 109.09%, and the margin is 8.33%.
- Parlays. The margin of each leg multiplies. Two 50/50 legs at −110 pay 1.909 × 1.909 = 3.645 times the stake, where fair odds would pay 4.00. The book keeps 8.9% of the money bet on average. Three legs pay 6.958 instead of 8.00, so the book keeps 13.0%.
Where Polymarket's fee is
On Polymarket you buy shares. A share costs its price and pays $1 if it wins. The fee is shown on each instant buy, and on sports markets it uses this formula:
fee = 0.05 × shares × price × (1 − price)
Price is in dollars, so 50¢ = 0.50. Here is the fee on a $100 bet at four prices:
| Price | Shares for $100 | Fee | Fee as a share of the bet |
|---|---|---|---|
| 5¢ | 2,000 | $4.75 | 4.75% |
| 20¢ | 500 | $4.00 | 4.00% |
| 50¢ | 200 | $2.50 | 2.50% |
| 80¢ | 125 | $1.00 | 1.00% |
Cheap shares pay a larger part of the bet in fees. A limit order that waits for its price pays no fee, and when it is taken it gets a share of a daily pool: 15% of the fees on that sports market, split among the waiting orders that were taken. Rates for other kinds of markets are on our Polymarket fees page.
There is a second cost. When you buy instantly, you pay the lowest price someone is selling at, and that price sits above the highest price someone is buying at. On a busy market the gap can be 1¢. On a quiet market it can be several cents. A sportsbook has no separate gap: everything is inside the odds.
Same bet, side by side
To turn a Polymarket price into decimal odds, divide 1 by the price: 50¢ is 1 ÷ 0.50 = 2.000. With the fee, one share costs price × (1 + 0.05 × (1 − price)). The odds after the fee are 1 divided by that cost, and that cost is also the share of bets you need to win to break even.
| Price | Odds before fee | Cost of one share with fee | Odds after fee | Break-even |
|---|---|---|---|---|
| 20¢ | 5.000 | 0.20 × 1.04 = $0.208 | 4.808 | 20.80% |
| 50¢ | 2.000 | 0.50 × 1.025 = $0.5125 | 1.951 | 51.25% |
| 80¢ | 1.250 | 0.80 × 1.01 = $0.808 | 1.238 | 80.80% |
Now the same three bets at a sportsbook with the −110 margin of 4.76%, if the book spreads that margin over both sides in proportion to the chances. Each cell is the share of bets you need to win to break even.
| Real chance of winning | 20% | 50% | 80% |
|---|---|---|---|
| Sportsbook, −110 margin | 20.95% | 52.38% | 83.81% |
| Polymarket, instant buy at that price | 20.80% | 51.25% | 80.80% |
| Polymarket, instant buy 1¢ higher | 21.83% | 52.25% | 81.77% |
| Polymarket, limit order at that price | 20.00% | 50.00% | 80.00% |
At 50%, an instant buy 1¢ above the fair price breaks even at 52.25%, close to the 52.38% of a −110 bet. A book at −105 breaks even at 51.22%. At 20%, a 1¢ gap adds more than the sportsbook margin. At 80%, the Polymarket fee is lower. Real books do not always spread the margin evenly, and a limit order may never trade, so read the table as math, not as a forecast.
What makes each one cost more or less
- Sportsbook: the market. The margin depends on the book and the bet. Main lines on big games have the lowest margins; parlays multiply the margin of every leg.
- Polymarket: the price. The fee is largest as a share of the bet on cheap shares, and smallest near 100¢.
- Polymarket: how you buy. An instant buy pays the fee and the gap. A limit order pays no fee, but it may never trade, and the price can move away from you.
- Polymarket: winning and selling. Winning shares pay $1 each with nothing taken out; see does Polymarket take a cut of winnings. Selling before the end pays a second fee; see cashing out early on Polymarket.
- Polymarket: money paid back. Since 28 May 2026 Polymarket returns 3% to 50% of the fee on instant buys, depending on your level over 30 days. Read does Polymarket give any fees back?
Neither one adds up the fee for you. A sportsbook shows the odds you got, not the margin inside them. Polymarket shows the fee on each trade, but no total, and the profit or loss on your profile already has the fees taken out. The free check above shows every fee you paid in the last 30 days, to the cent.
Questions
Does Polymarket have vig?
Not in the sportsbook sense: the price is set by other traders, not by a book that adds a margin to both sides. Instead, an instant buy pays a fee shown on the trade, and the buyer also pays the gap between the buy and sell prices. On sports markets the fee is 0.05 × shares × price × (1 − price), and a limit order that waits for its price pays no fee.
Is Polymarket cheaper than a sportsbook?
It depends on the bet. On a 50/50 game, an instant buy 1¢ above the fair price breaks even at 52.25%, against 52.38% for a −110 bet and 51.22% for a −105 bet. On cheap shares with a wide gap, Polymarket can cost more; on expensive shares, it can cost less.
How do I convert Polymarket prices to odds?
Divide 1 by the price in dollars: 20¢ is 5.000, 50¢ is 2.000 and 80¢ is 1.250 in decimal odds. For an instant buy on a sports market, first add the fee to the price: price × (1 + 0.05 × (1 − price)). At 50¢ that is $0.5125, so the odds after the fee are 1.951.
Do I pay a fee if I win on Polymarket?
No. Each winning share pays $1 and nothing is taken from the payout. The fee was paid earlier, when you bought instantly, and again if you sold instantly before the end. More in does Polymarket take a cut of winnings.
Why is my break-even higher than the price?
Because an instant buy costs the price plus the fee. At 50¢ on a sports market, one share costs $0.50 plus $0.0125 in fees, so you need to win 51.25% of such bets to break even, not 50%. To see what the fees added up to on your own bets, read how much have I paid in Polymarket fees.