What is implied probability in prediction markets?
Implied probability is the single most important concept in prediction markets. It is the simple observation that the price of a YES share, expressed as a decimal between 0 and 1, is the market's best estimate of how likely the underlying event is to occur.
What is implied probability in prediction markets?
The basic reading
A YES share trading at $0.62 implies the market believes there is about a 62% chance the event will happen. A YES share at $0.08 implies an 8% chance. Because YES and NO shares sum to ~$1, the NO share at the same moment would trade at around $0.38, implying a 38% chance the event does not happen — and 62% + 38% = 100%, as expected.
Why it works
If the "true" probability were higher than the market price, rational traders would buy YES until the price moved up. If it were lower, they would sell YES until the price moved down. Profit-motivated arbitrage keeps the price close to the collective best estimate — which is why liquid prediction markets tend to outperform polls, pundits, and expert panels on many types of questions.
Where the reading breaks down
Implied probability is only as reliable as the market is liquid. In thin markets, a single large trader can move the price without any new information. Fees also matter: if a venue charges a 7% take on winnings, the "true" implied probability is slightly higher than the raw price suggests. And for long-dated markets, the price partially reflects the cost of capital — traders discount future payouts, nudging prices below the actual probability.
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