How to read prediction market odds like a probability
A 62¢ contract is not a price — it's a crowd's forecast. Here's how to translate cents into probability, and where that translation quietly breaks down.
The one-line version
On Polymarket, Kalshi, and most other prediction markets, a YES contract pays out $1 if the event happens and $0 if it doesn't. So the price of that contract — say 62¢ — is the market's implied probability of the event: about 62%.
That single fact is what makes prediction markets so readable compared to sportsbook odds or spread betting. You don't need to convert from American odds or back out a decimal. The price *is* the forecast.
YES and NO should add up to a dollar
Every market has two sides. If YES trades at 62¢, NO should trade near 38¢, because exactly one of them will be worth $1 at resolution. When the two sides sum to meaningfully more than $1, you're looking at the spread — the gap between what buyers will pay and what sellers will accept.
That gap is your real cost of entry. A market quoting YES at 64¢ and NO at 40¢ is charging you roughly 4¢ to take either side. On a contract you expect to be worth $1, 4¢ is a 4% haircut before you're right about anything.
Where the probability reading breaks down
The price-as-probability translation is clean in theory and leaky in practice. A few common distortions:
- Thin volume. A market with $2,000 of total volume reflects a handful of opinions, not a crowd. The price is a quote, not a consensus.
- Time value. Money locked in a contract that resolves in 14 months has an opportunity cost, which pushes long-dated YES prices slightly below their true probability.
- The longshot bias. Contracts trading under about 10¢ tend to be persistently overpriced — people like cheap lottery tickets, on prediction markets as everywhere else.
- Ambiguous resolution criteria. If reasonable people disagree about what counts as the event happening, part of the price is a bet on the resolver, not on the world.
What to do with this
Before you take a position, do the arithmetic out loud: at this price, the market thinks there's an X% chance. Do I actually believe the real number is meaningfully different — enough to clear the spread and the fees?
If you can't name the number you disagree with and why, you don't have an edge. You have an opinion. Those are not the same trade.