How to Read Prediction-Market Odds
On a prediction market, the price of a contract is the market's estimate of how likely an event is. A "Yes" share trading at 63 cents means traders, collectively, are pricing the outcome at roughly a 63% chance. This guide explains how to convert price into probability, how to read a move, what volume and liquidity tell you, what a gap between Polymarket and Kalshi means, and the mistakes that lead people to misread the number. Prediction-market prices are crowd-sourced probability estimates, not guarantees or advice.
Price is implied probability
Prediction-market contracts settle at either $1 (the event happened) or $0 (it did not). Because of that, the current price reads directly as a probability. A contract at $0.70 implies about a 70% chance; one at $0.25 implies about 25%. The formula is simply price multiplied by 100.
Yes and No prices are complementary and add up to roughly $1. If Yes trades at $0.63, No trades near $0.37. In practice they sum to slightly more than $1 because of the bid-ask spread, the gap between the best buying and selling price. Unlike a sportsbook, which builds a house margin into its odds, an exchange-style prediction market sets price through supply and demand among traders, so one number maps to one probability without bookmaker math.
Reading a move or a swing
A price change is a change in the crowd's probability estimate, usually triggered by new information: a poll, an earnings report, a court ruling, a candidate dropping out. A contract jumping from $0.40 to $0.70 means the implied chance rose from 40% to 70%.
Ask two questions about any swing. First, did real news arrive, or did one large order push a thin market around? Second, did the move hold or snap back? A durable repricing after a clear event is more meaningful than a spike that reverts within minutes. Watch the size of the move relative to the contract's normal daily range, and check whether other related markets moved in the same direction.
Volume, liquidity and open interest
These three numbers tell you how much to trust the price. Volume is how much has traded over a period; it shows current activity and whether a price move attracted new participants. Open interest is the total number of contracts still outstanding and not yet settled, a gauge of how much money is committed to the market overall.
Liquidity is the depth of resting buy and sell orders. High liquidity means tight spreads and prices that hold up; low liquidity means wide spreads and prices that can lurch on a single order. A market with heavy volume and deep order books is a more reliable probability reading than a thin one that may sit untraded for hours. Treat prices on low-volume, low-open-interest contracts with caution: they move erratically and are easier to push.
What a Polymarket-Kalshi gap means
Polymarket and Kalshi are two of the largest venues, and they often list the same event. Polymarket, founded in 2020 by Shayne Coplan, settles in the stablecoin USDC; in November 2025 it secured CFTC clearance to operate as a regulated U.S. exchange with intermediated access. Kalshi, founded in 2018 by Tarek Mansour and Luana Lopes Lara, launched in 2021 as a CFTC-regulated U.S. exchange and settles in dollars.
When the same outcome is priced differently across the two, the gap reflects different trader pools, fees, and liquidity rather than a guaranteed mispricing. Small gaps are normal. A persistent, large gap is worth noting: it usually means one venue is thinner or its contract is worded slightly differently. Always compare the exact resolution criteria before assuming two markets are measuring the same thing.
Common misreadings
Treating a probability as a prediction. A 75% market still resolves No one time in four; that is not a market being wrong, it is the lower-probability outcome occurring as expected over many events.
Trusting extremes too much. Research commonly finds a favorite-longshot bias: very unlikely outcomes tend to be overpriced and strong favorites slightly underpriced, with prices near 0% and 100% often the least reliable. Markets tend to be best calibrated in the rough 20%-to-80% range.
Reading a thin market as consensus. A price set by little money is not the wisdom of a crowd. Other traps: ignoring fees that erode the implied edge, and confusing a stale last-trade price with the live mid-market price.
Frequently asked questions
What does a 70% prediction market price mean?
It means the market estimates about a 70% chance the event resolves Yes. The contract pays $1 if it happens and $0 if it does not, so a $0.70 price reads directly as 70% implied probability. It is a crowd estimate, not a guarantee: roughly three times in ten, a 70% market still resolves No.
Why do Polymarket and Kalshi show different odds?
They have separate trader pools, fees, settlement currencies, and liquidity, so the same event can price slightly differently. Small gaps are routine. A large, persistent gap usually signals that one venue is thinner or that the two contracts have subtly different resolution rules. Compare the exact wording before assuming a true mispricing exists.
What is the difference between volume and open interest?
Volume is how many contracts traded over a period and reflects current activity. Open interest is the total number of contracts still outstanding and unsettled, reflecting how much money is committed overall. High volume signals an active price; high open interest signals a deep, established market. Together they indicate how reliable a price is.
Are prediction market odds accurate?
Studies generally find prediction markets are well calibrated, especially for outcomes in the roughly 20%-to-80% range, where prices tend to track real frequencies closely. Accuracy often degrades at the extremes due to favorite-longshot bias, where very unlikely events tend to be overpriced. Thinly traded markets are far less reliable than liquid ones.
How do I read a sudden swing in the odds?
A swing is a change in the crowd's probability estimate, usually from new information like a poll or ruling. Check whether genuine news drove it or a single large order pushed a thin market, and whether the move held or reverted. Durable repricing after a clear event is more meaningful than a brief spike.