A prediction market contract priced at 73 cents is telling you something specific: the market thinks there is a 73 percent probability the event happens. That one-line interpretation is the foundation of the entire asset class, but it hides a dozen subtleties that separate amateur traders from the sharps who consistently book profits. This guide walks through everything you need to read prediction market prices the way a professional does, from basic contract mechanics to the subtle tells that reveal when a market is mispriced.
What a Contract Price Actually Means
On Kalshi, Polymarket, and every other major event contract exchange, a binary contract pays exactly one dollar if the stated event resolves YES and zero if it resolves NO. Because the payout is a clean one dollar, the price of the contract is a direct probability estimate. A contract at 42 cents is the market’s collective bet that there is a 42 percent chance the event happens. A contract at 91 cents implies a 91 percent chance. There is no vig baked into the odds the way a sportsbook builds in a hold, which is why prediction markets are often described as the cleanest probability estimate available on any real-money venue.
The YES and NO sides of a binary market always sum to one dollar, minus any bid-ask spread. If the YES side is bid at 67 and offered at 69, the NO side will be bid at 31 and offered at 33. A trader who thinks the true probability is 80 percent buys YES at 69 and holds. A trader who thinks the true probability is 50 percent sells YES or buys NO at 33. The decision is always a comparison of the market’s number to your own.
Converting Prices, Odds, and Probabilities
Professional traders move fluently between three representations of the same information. Knowing the conversions lets you compare a prediction market price to a sportsbook line, an options implied probability, or a forecaster’s stated confidence.
| Contract Price | Implied Probability | American Moneyline | Decimal Odds |
|---|---|---|---|
| 10 cents | 10 percent | +900 | 10.00 |
| 25 cents | 25 percent | +300 | 4.00 |
| 50 cents | 50 percent | Even (+100 / -100) | 2.00 |
| 67 cents | 67 percent | -203 | 1.49 |
| 75 cents | 75 percent | -300 | 1.33 |
| 90 cents | 90 percent | -900 | 1.11 |
The formulas are simple. Decimal odds equal 1 divided by the probability. American moneyline is plus (100 divided by probability minus 100) for underdogs under 50 percent, and minus (probability divided by one minus probability times 100) for favorites over 50 percent. Internalize these so you can spot a sportsbook offering minus 350 on a market Kalshi has at 72 cents, which translates to 77.8 percent versus 72 percent, and recognize instantly that the prediction market is the better buy.
Why the Bid-Ask Spread Matters More Than the Last Price
The number displayed as the “price” on most interfaces is the last traded price, and that can be seconds, minutes, or hours old in a quiet market. What you can actually transact at is the current bid-ask spread, and the width of that spread tells you more about the market than the midpoint does.
A one-cent spread between bid and ask signals a liquid, well-arbitraged market where the true probability is almost certainly within half a cent of the midpoint. A ten-cent spread signals a thin market where the midpoint is a suggestion, not a price, and your trade will either cross the full spread or sit unfilled. Three practical rules follow from this.
- Never pay the ask in a thin market without checking depth. If you need to buy 5,000 contracts and only 400 are offered at the inside ask, you will walk the book up and get a materially worse average fill.
- Use limit orders at the midpoint or better. In markets where the spread exceeds two cents, your limit at the midpoint will frequently fill as other traders cross you.
- Treat the spread as a tax on your edge. If you think a contract trading at 60 offer and 56 bid is worth 58, you have no edge after fees. A real edge means your fair value is outside the spread.
Volume, Open Interest, and the Lies Thin Markets Tell
Two markets can show the same 68 cent price and be completely different trades. A contract with ten million dollars of open interest and a one-cent spread is a serious probability estimate aggregating real money from real forecasters. A contract with four hundred dollars of open interest and a four-cent spread is a few random orders that have not been arbitraged yet. The price is information in the first case and noise in the second.
Open interest is the total dollar value of contracts currently outstanding. Volume is the dollar value traded over a given period. High open interest with low current volume means the market has settled into a consensus. Low open interest with high current volume means a price is actively being discovered. Low open interest with low volume means the price is whatever the last casual trader paid, and it does not deserve much weight in your forecasting.
The practical test is to ask whether the market has been stress-tested. If a contract at 73 cents represents one hundred thousand dollars of open positions on both sides, dozens of traders have independently concluded 73 is roughly right. If the same price represents five hundred dollars of open positions, you are looking at three people’s opinion.
Reading Probability Changes Over Time
Price movement is where most of the real information lives. A market that holds steady at 55 cents for weeks is telling you the balance of evidence has not shifted. A market that moves from 55 to 72 in forty-eight hours is telling you new information has arrived and been absorbed. The direction and speed of movement matter more than the absolute level.
Pay attention to how markets respond to specific events. A debate performance that moves a presidential market three cents is a muted reaction; the market has already priced in the candidates’ likely performance. A policy announcement that moves a Fed rate market twelve cents is a shock; the market was positioned for a different outcome. Over time, you will build intuition for which events are already priced and which are genuine surprises.
One warning: short-term price movements are noisy, and traders routinely overreact to cable news cycles. A contract that jumps six cents on a single tweet and then drifts back over the following week was not responding to fundamentals. Our guide on the best prediction markets of 2026 covers how volume patterns differ between platforms and which markets tend to reflect genuine information versus media-driven noise.
Mistakes That Give Away Your Edge
Three errors show up constantly in amateur trading accounts and reveal that a trader is reading prices wrong.
The first is treating certainty as free money. A contract at 92 cents looks like a sure thing, and traders pile in expecting an eight-cent gain. In reality, 8 percent of 92 cent contracts resolve NO, and when they do, you lose the entire 92 cents. The expected return on buying at 92 is exactly zero if the market is fairly priced, and negative after fees. Favorites are not free money; they are leveraged exposure to tail risk.
The second is anchoring on the last traded price. If a contract last traded at 45 cents a week ago and the current best offer is 52, the market is 52, not 45. Traders who refuse to pay 52 because they anchored on 45 miss trades that were fairly priced all along.
The third is confusing confidence with edge. You can be 90 percent confident a candidate will win and still have no trade if the market already prices the candidate at 92. Edge is the gap between your probability estimate and the market’s, not the strength of your opinion. A trader with a disciplined 2 cent edge on hundreds of contracts outperforms a trader with vague conviction on a single bet.
Putting It Into Practice
Reading prediction market probabilities well is a skill you build one contract at a time. Start by funding a small account on Kalshi for CFTC-regulated US markets, or Polymarket for broader global coverage. Pick two or three markets you follow closely, watch the prices move for a week before placing a single trade, and build your intuition for what moves the number and what does not. The traders who book consistent profits are not the ones with the strongest opinions. They are the ones who read prices the most clearly, size their positions accordingly, and only trade when their fair value meaningfully differs from the market’s.