The Simple Rule: Price Equals Probability
Reading prediction market probabilities is simpler than it sounds. The price of a share is the implied probability of the outcome. A share trading at $0.80 implies an 80% probability. A share at $0.40 implies a 40% probability. A share at $0.05 implies a 5% probability.
This is the single most important thing to understand about prediction markets. Once you internalise the rule, prices stop looking like dollar amounts and start looking like probability estimates. A market price moving from $0.50 to $0.65 is the same as the implied probability moving from 50% to 65%. The two ways of describing the move are interchangeable.
The rule works because of how the contracts pay out. Each share pays $1 if the outcome resolves correctly and $0 if not. If a contract trades at $0.80 and the underlying outcome resolves yes 80% of the time, traders are roughly indifferent between buying and selling at that price (the expected value matches the cost). The market settles at the price that reflects aggregate trader beliefs about probability.
For background on the underlying mechanics see our what are prediction markets guide and our how prediction markets work guide.
How to Interpret 80c Per Share
Let us walk through what a specific price actually means. Suppose you see a market on whether the Fed will cut rates by 25 basis points at the next meeting trading at $0.80 per share. What does the price tell you?
The market is implying an 80% probability of a 25 basis point cut. Said differently: if you bought 100 contracts at $0.80 each (total cost $80), the market thinks you would win $100 (the resolution payout) about 80% of the time. The other 20% of the time, you would lose your $80 stake. The expected value of this trade at the market price is $0.00, which is exactly what the market price implies for a fair-priced contract.
If you personally believe the probability is higher than 80% (say you think there is a 90% chance), the trade has positive expected value for you at $0.80. Buying at $0.80 when you believe 90% gives you positive expected value of $0.10 per contract. If you personally believe the probability is lower than 80%, the trade has negative expected value. You should sell or not trade.
Most importantly, the market price is the consensus estimate of all active traders weighted by their conviction (which shows up as how much they are willing to trade at the price). The price is not a single trader's opinion. It is the aggregated view of everyone with skin in the game. This aggregation is the source of prediction market accuracy.
Implied Probability and Multiple Outcomes
Implied probability gets slightly more complicated when a market has more than two possible outcomes. An election market with three candidates needs three contracts (one for each candidate winning), and the prices of all three contracts should sum to roughly $1.00.
If candidate A trades at $0.50, candidate B trades at $0.35, and candidate C trades at $0.10, the total is $0.95. The 5 cent gap from $1.00 reflects the implicit probability that none of the three named candidates win (an outsider, drop-out, or other resolution). The market is telling you the implied probabilities are 50%, 35%, 10%, and 5% other.
The same principle applies to all multi-outcome markets. Sum all contract prices on a single market to verify they roughly equal $1.00. The small gap below $1.00 represents either edge cases or trader preference for liquidity. The prices should not sum to materially more than $1.00; if they do, that is an arbitrage opportunity.
For binary markets (yes/no contracts), the math is simpler. A yes contract at $0.65 implies a 65% probability of yes. The corresponding no contract trades at $0.35 (representing 35% probability of no). The two should sum to roughly $1.00 minus any small spread or platform-specific fee adjustment.
What Calibration Means
Calibration measures whether the implied probabilities from prediction markets match real outcome frequencies. A perfectly calibrated market's events at 70% probability happen 70% of the time across many similar markets. A poorly calibrated market's 70% events might only happen 60% of the time, indicating the market consistently overprices these outcomes.
Liquid prediction markets tend to be reasonably well calibrated. Across many flagship political and economic events, prediction markets on Kalshi, Polymarket, and similar platforms have shown calibration that matches or beats traditional polling and forecasting models. The accuracy advantage holds in academic studies dating to the 1980s and continues in modern cycles.
Some bias appears at the extremes. Long-shot bias means events at very low probability (1-5%) often happen even less frequently than the implied price suggests. Inverse bias appears at very high probabilities (95-99%) where outcomes happen more often than implied. The biases are well-documented and provide trading opportunities for users who recognise them.
Practically, this means you can take prediction market prices as approximate probability estimates with confidence on liquid mainstream markets. On thin markets or extreme probabilities, treat the prices with more scepticism. For more on the accuracy debate see our how accurate are prediction markets guide.
Practical Examples From Real Markets
Let us look at how price-equals-probability works in real markets you might encounter.
Election example: A presidential contract trading at $0.55 implies a 55% probability of winning. If you watch the price move from $0.55 to $0.65 over the following week, the implied probability moved from 55% to 65%. The market is telling you that something happened during the week (a strong debate performance, a positive polling shift, a major endorsement) that increased traders' aggregate confidence in the outcome by 10 percentage points.
Federal Reserve example: A Fed rate decision contract on whether the FOMC will cut by 25 basis points trades at $0.85 in the days before the meeting. The implied probability is 85%. If the contract trades at $0.95 the morning of the meeting, the market is reflecting near-certainty about the cut, possibly due to clear recent Fed messaging. If the contract drops to $0.65 after a hawkish FOMC member comment, the implied probability has dropped to 65%, signalling new uncertainty about the decision.
Sports example: A NFL game outcome market trades at $0.40 on the underdog team. Implied probability of the underdog winning is 40%. After the favourite's starting quarterback gets injured during warmups, the underdog price might jump to $0.60 (implied probability 60%). The price move reflects the market's quick adjustment to the new information.
In each case, watching the price gives you a real-time probability estimate. Watching how the price moves with news flow shows how the market is interpreting and pricing new information. The price is information, not just a number.
FAQ
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