How Prediction Market Probabilities Work

Most prediction markets list binary contracts. Each contract settles at a fixed value, commonly $1, if a stated event happens, and at $0 if it does not. Because the payoff is fixed, the price a contract trades at can be read as the market’s implied probability that the event happens.

If a "Yes" contract trades at 62 cents, the simplest reading is that the market, in aggregate, assigns roughly a 62% chance to the event. The matching "No" contract should trade near 38 cents, since the two sides together cover every outcome.

That reading is a useful starting point, not a guarantee. The rest of this page explains what a price actually represents and when it can drift away from a clean probability.

The basic conversion is direct: divide the price by the settlement value. On a contract that pays $1, a price of $0.25 implies 25%. Some venues quote in cents, others in decimals, but the math is the same.

Consider a contract asking whether a monthly inflation figure will come in above a threshold. If Yes trades at 40 cents and No at 62 cents, the two sides add to 102 cents. The extra 2 cents is friction: fees, spread and the cost of providing liquidity. A common way to recover a cleaner estimate is to normalize, dividing 40 by 102 to get about 39%.

A market rarely has one price. There is a bid, the most a buyer is currently willing to pay, and an ask, the least a seller will accept. The gap between them is the spread.

On an active contract the spread may be 1 or 2 cents, and the midpoint between bid and ask is a reasonable probability reading. On a thin contract the bid might be 20 cents and the ask 45 cents. In that case no single number is a trustworthy probability; the market is telling you only that the answer is somewhere in a wide range.

The last traded price can be misleading for the same reason. A single small trade hours ago says little about where the market stands now.

Prices aggregate the views and constraints of the people trading, and several forces can push them away from an unbiased estimate:

Suppose a contract on a Kalshi-style exchange asks whether a commodity will close above a given level by Friday. The Yes bid is 54 cents, the Yes ask is 57 cents, and several thousand contracts have traded today.

The midpoint is 55.5 cents, so a reasonable reading is about a 55% implied probability. The spread is narrow and volume is healthy, so that reading is fairly reliable. If the same contract showed a 30 cent bid and a 70 cent ask with almost no volume, the honest reading would be "somewhere between 30% and 70%, with little evidence either way."

Implied probability is best treated as one input, not a verdict. It tells you what the market currently prices, which is valuable context. It does not tell you why, and it does not account for evidence the market may be underweighting.

That is where independent analysis comes in. Comparing an evidence-weighted view against the market price is the subject of model confidence vs market probability. If you want to look at a specific market, Market Console lets you check a market’s structure and run a QSE analysis on it. For market-wide context on where activity is concentrated, see Market Landscape, and for definitions of terms used here, the glossary.

Nothing on this page is financial advice. Prices and probabilities describe uncertainty; they do not remove it.