--- title: "How to tell if a Polymarket price is fair" canonical: "https://0xinsider.com/learn/how-to-tell-if-a-polymarket-price-is-fair" datePublished: "2026-09-28" dateModified: "2026-09-28" description: "How to judge a Polymarket sports or esports price: implied probability, the spread and book depth, overround across outcomes, how the price moved, and closing line value." --- # How to tell if a Polymarket price is fair Last updated: 2026-09-28 Canonical: https://0xinsider.com/learn/how-to-tell-if-a-polymarket-price-is-fair A Polymarket price is a probability in cents. On sports markets it is usually close to fair: large buys from April to September 2026 paid 60.6¢ and won 60.7% of the time. Five checks show when a price is not. ## The short answer A price is fair when it matches the chance the outcome happens. Nobody can read that chance directly, so you judge the price by how it was made: what you would actually pay, how deep the book is, whether the outcomes add up to 100%, how the price moved, and who holds each side. After the game, closing line value grades the price you got. The chart above is the base rate. In a study of large Polymarket sports buys from April 2 to September 11, 2026, the share of buys that won tracked the price paid in every bucket from 20¢ up. The exception was under 10¢, where buyers overpaid, covered at 0xinsider.com/learn/favorite-longshot-bias-explained. So a sports price starts out as a good estimate, and each check below looks for a reason this one is not. 0xinsider covers Polymarket only. It does not compare prices across venues. It shows both sides of every game with their prices, which side the profitable wallets hold, and the closing line value of every Pick of the Day on a public record. ## Read the price as a probability Every Polymarket share is priced between $0 and $1 and pays $1 if its outcome happens, so a price in cents reads as a probability in percent. A team at 62¢ is a 62% chance. That is the implied probability, defined at 0xinsider.com/learn/glossary/implied-probability. Yes and No on the same market are two sides of one dollar. Polymarket's documentation describes a first trade as a buy of Yes at 60¢ matched with a buy of No at 40¢: together they make $1, which becomes one Yes share and one No share. A fair Yes price therefore fixes a fair No price. ## Check 1: the price you pay The price Polymarket displays is the midpoint between the best bid and the best ask. When the spread is wider than 10¢, Polymarket shows the last traded price instead. Neither is what you pay. A buy fills at the ask and a sale fills at the bid, and a taker pays a fee on top. So judge the ask, not the headline. A 60¢ midpoint with a 58¢ bid and a 62¢ ask costs 62¢ to buy, and the outcome has to be better than 62% for the buy to be fair to you. The guide at 0xinsider.com/learn/how-to-read-polymarket-order-book reads bids, asks and the spread, and 0xinsider.com/learn/polymarket-fees-explained has the fee formula. ## Check 2: how deep the book is The best ask holds a set number of shares. An order larger than that fills at the next price up, and the next, so your average price is worse than the quote. That gap is slippage, and 0xinsider.com/learn/glossary/market-depth explains how to read it before you size an order. Depth also tells you whose price it is. A price on a book with many resting orders at every level is set by many traders. A price on a thin book can be one participant's quote, and one order can move it. Trust a thin price less, whichever way it points. ## Check 3: add up every outcome Each outcome has its own order book, so the prices to buy every outcome can add up to more than 100%. The excess is the overround: what it costs to take every side at once. A two-way game that adds to 101% or 102% is tight. A three-way soccer market at 110% carries a wide margin on at least one outcome. The guide at 0xinsider.com/learn/why-prediction-market-odds-exceed-100-percent explains where the excess comes from. To read each price with the margin taken out, divide it by the total. The odds calculator at 0xinsider.com/tools/odds-calculator does that for 2 to 64 outcomes and states the no-vig fair price in cents. The no-vig number removes the margin in proportion. It adds no information about who wins. ## Check 4: how the price got there A price that moved because a lineup or an injury became known reflects the news. A price that moved because one large order walked through a thin book can come back once the book refills. Before you trust a move, look at what traded behind it: the large-trade feed at 0xinsider.com/trades shows each large fill with the buyer's grade beside it. Timing matters as much as direction. The guide at 0xinsider.com/learn/line-movement-sports-betting-explained shows when the money arrives on Polymarket sports markets and which windows before and during a game were priced well. ## Check 5: who is on each side Every Polymarket trade has a public wallet behind it, and 0xinsider grades wallets on settled P&L. Each game on a sports board, from 0xinsider.com/sports, shows both sides with their prices and which side the profitable wallets hold. With Pro the split is live. Without Pro it shows on a delay, and a game with no reading that old shows the money total and wallet count with the split locked. With Pro, a game where the profitable wallets lean against the price also shows the gap in points between their share of the money and the probability the price implies. It measures positioning. It is not a win probability or an expected return, and the guide at 0xinsider.com/learn/how-to-find-sharp-money-polymarket-sports shows how to read the profitable wallets' bars against the price. ## Grade the price afterwards with closing line value The result of one game says little about the price. Closing line value compares your entry with the last price before kickoff. If the market moved toward your side after you bought, you got the better number. 0xinsider.com/learn/closing-line-value has the formula and the fee adjustment. Pick of the Day runs this test in public. Each pick is released an hour before its kickoff at a frozen price that is never rewritten. Where the capture succeeds, the record stores the last valid price before kickoff beside it. 0xinsider.com/pick-of-the-day/stats shows the average closing line value and how many settled picks it covers. ## What 0xinsider does not do 0xinsider does not compare Polymarket prices with sportsbooks or other exchanges, and it publishes no fair price for a game of its own. If you hold a line from another venue, the odds calculator converts it to a no-vig price in cents, and the comparison is yours to make. That line carries only what its venue knew, and a Polymarket price still has its spread and fee to pay. ## Frequently Asked Questions Is a Polymarket price the probability of the outcome? It is the market's implied probability. A share pays $1 if its outcome happens, so a 62¢ price reads as a 62% chance. In a study of large sports buys from April to September 2026, win rates tracked prices from 20¢ up, and buyers under 10¢ overpaid. Why is the price I pay different from the price shown? Polymarket displays the midpoint between the best bid and the best ask, or the last traded price when the spread is wider than 10¢. A buy fills at the ask, a large order can fill at several prices, and a taker pays a fee. Why do the outcome prices add up to more than 100%? Each outcome has its own order book, so the prices to buy every outcome include each book's spread. The excess is the overround. Divide each price by the total to remove it, or use the free 0xinsider odds calculator. Does 0xinsider compare Polymarket prices with sportsbooks or other exchanges? No. 0xinsider covers Polymarket only. Its odds calculator converts a line from another venue into a no-vig price in cents so you can make the comparison yourself. What does 0xinsider show about whether a price is fair? Both sides of every game with their prices, which side the profitable wallets hold (live with Pro, on a delay without), the large trades behind a move, and the closing line value of every Pick of the Day on a public record.