A prediction market price is a probability. That one idea is the whole subject: if a contract trades at 63¢, the market is saying there is roughly a 63% chance the event happens. Sportsbook odds hide the same information behind fractions and plus-minus numbers, which is why the two look so different at a glance.
Price to probability
Contracts on Polymarket and Kalshi pay out $1 if the event happens and $0 if it doesn't. So the price you pay is the market's implied probability, in cents:
Implied probability = contract price. A contract at $0.63 implies a 63% chance. A contract at $0.08 implies 8%.
Your profit follows directly. Buy a YES contract at 63¢, and if the event happens you receive $1 — a profit of 37¢ on 63¢ risked, or about 59%. If it doesn't happen, you lose the 63¢. The cheaper the contract, the bigger the payoff and the less likely the market thinks it is.
Worked example
| Price paid | Implied chance | Profit if YES | Return |
|---|---|---|---|
| $0.90 | 90% | $0.10 | +11% |
| $0.63 | 63% | $0.37 | +59% |
| $0.25 | 25% | $0.75 | +300% |
| $0.05 | 5% | $0.95 | +1,900% |
YES and NO are two sides of the same price
Every market has a YES side and a NO side, and they add up to $1. If YES trades at 63¢, NO trades at 37¢. Buying NO at 37¢ is exactly the same bet as selling YES at 63¢. This is why you never need a "lay" market or a separate bookmaker to bet against something — the other side is always available at the complementary price.
Converting to and from sportsbook odds
If you are used to sportsbook formats, these are the conversions. Let p be the probability as a decimal (63¢ = 0.63).
| Format | Formula | At 63¢ |
|---|---|---|
| Decimal odds | 1 ÷ p | 1.59 |
| Fractional odds | (1 − p) : p | 4/7 |
| American (favourite, p > 0.5) | −100 × p ÷ (1 − p) | −170 |
| American (underdog, p < 0.5) | 100 × (1 − p) ÷ p | — |
Going the other way, decimal odds of 2.50 imply 1 ÷ 2.50 = 0.40, or a 40% chance — a contract price of 40¢.
Why the sportsbook number is always worse
Sportsbook odds include the bookmaker's margin, known as the overround or vig. Price up both sides of a two-way sportsbook market and the implied probabilities sum to more than 100% — often 104–110%. That excess is the house edge, and it is the reason the implied probability from a sportsbook is not a clean estimate of anything.
On a prediction market, YES and NO sum to $1 by construction. The platform earns from trading or settlement fees rather than from skewing the line, so the price is a much more direct reading of what participants collectively believe.
What moves a price
- News. New information gets priced in within minutes on liquid markets.
- Time. As the resolution date nears, prices drift towards 0 or 100 as uncertainty resolves.
- Liquidity. A market with little money in it can swing on a single order, so a thin market's price is a weak signal. Check the volume before reading much into it.
- The spread. The gap between the best buy and sell price is a real cost. On quiet markets it can be several cents wide.
How accurate are they?
The honest answer is: well calibrated in aggregate, not infallible in any single case. Across many markets, things priced at 70% do tend to happen around 70% of the time — that is what "calibrated" means, and it is the strongest argument for reading prediction markets at all. But a calibrated 70% still fails three times in ten, and thin or newly listed markets are much noisier than headline ones.
A price is not a prediction of what will happen. It is the current consensus estimate of how likely it is, and it will be wrong a predictable fraction of the time.
Comparing prices across platforms
The same question is often listed on more than one platform, and the prices are not always the same. A 3–4 cent gap on the same contract means the two sets of traders disagree — or that one market has not caught up with the news yet. Comparing them is the entire reason this site exists, and the cards below are live.
World
Polymarket
Will Russia and Ukraine hold any diplomatic meeting by October 31, 2026?
Politics
Polymarket
2026 Balance of Power: R Senate, R House
Sports
Polymarket
Will Donald Trump win the Nobel Peace Prize in 2026?
Sports
Polymarket
Will Kylian Mbappé win the 2026 Ballon d'Or?
Polymarket
Will the Fed increase interest rates by 25 bps after the October 2026 meeting?
Polymarket
Will there be no change in Fed interest rates after the October 2026 meeting?
Common questions
Does a 90¢ price mean it is a safe bet?
It means the market thinks there is a 90% chance. One in ten such contracts still settles at zero, and because you are risking 90¢ to make 10¢, a single loss wipes out the gains from nine wins.
Why don't YES and NO add up to exactly $1 on screen?
Displayed prices are usually the last trade or the mid-point of the order book, so rounding and the bid-ask spread can leave a cent or two unaccounted for. The underlying contracts still settle at $1 and $0.
What happens if the event is ambiguous?
Each market has written resolution rules naming the source that decides the outcome. Those rules, not common sense, determine the payout — always read them before trading, because the edge cases are where disputes happen.