Event contracts, binary outcomes, order books, and implied probability. The foundational knowledge you need before placing a single trade.
A prediction market is an exchange where you buy and sell contracts that pay out based on whether a real-world event happens. Each contract is binary: it resolves to $1 if the event occurs, and $0 if it doesn't. The price of the contract at any moment reflects the market's collective estimate of the probability.
If you buy a contract at $0.35, you're saying: "I believe there's a greater than 35% chance this happens." If the event occurs, you receive $1 — a profit of $0.65 on your $0.35 investment. If it doesn't, you lose your $0.35.
The contract price = the market's implied probability. A contract trading at $0.72 implies a 72% chance of the event occurring. Your job as a trader is to find contracts where your estimated probability differs meaningfully from the market price.
Let's say it's the morning of a Bundesliga match — Borussia Dortmund vs. Bayern Munich. On Kalshi or Polymarket, you might see a contract like "Will Dortmund win?" priced at $0.28. This means the market implies a 28% probability of a Dortmund win.
If you believe Dortmund's actual chance is closer to 38% — perhaps because you know something about Bayern's injury situation that the market hasn't fully priced in — you buy the contract at $0.28. If Dortmund wins, you collect $1 per contract. If they lose, you lose your stake.
The critical distinction from traditional betting: you can sell your position before the event resolves. If Dortmund scores early and the contract price moves to $0.55, you can sell at a profit without waiting for the final whistle. This is trading, not betting.
Prediction markets operate with order books, just like stock exchanges. There are bids (buyers willing to pay a certain price) and asks (sellers willing to sell at a certain price). The spread between them is the bid-ask spread — and it's one of the costs of trading, alongside platform fees.
On liquid markets (major political events, popular sports), the spread is tight — often just 1–2 cents. On illiquid markets (niche questions, obscure events), the spread can be 10 cents or more, which significantly eats into any edge you might have.
A 5% edge means nothing if the bid-ask spread is 8%. Always check liquidity before committing capital. The most profitable prediction market traders focus on liquid markets where they can get in and out at reasonable prices.
Prediction markets sit at the intersection of several worlds:
Traders use them as a financial instrument — buying underpriced contracts, selling overpriced ones, building portfolios across uncorrelated events. The math is identical to options trading.
Hedgers use them to offset real-world risk. A German exporter worried about a trade policy change can buy contracts that pay out if the policy passes, partially offsetting their business loss.
Researchers and journalists use market prices as probability estimates. CNN displays Kalshi data on-air during elections. The Federal Reserve has published papers analysing prediction market accuracy.
Information consumers simply check prices to gauge what the collective wisdom thinks about upcoming events — from election outcomes to interest rate decisions.
| Platform | Type | Access | Key Feature |
|---|---|---|---|
| Kalshi | CFTC-regulated | US (KYC) | Only regulated PM in the US |
| Polymarket | Crypto-based | Global | Highest liquidity, widest markets |
| Metaculus | Forecasting | Global | Reputation-based, no real money |
| Manifold | Play money | Global | Anyone can create markets |
For a detailed comparison including sportsbooks and exchanges, see our Market Directory.
They are not sportsbooks. Sportsbooks set odds and take the other side of your bet. They profit when you lose and they limit you when you win. Prediction markets match buyers and sellers — the platform is neutral.
They are not gambling in the traditional sense. Yes, individual contracts are binary — but so are options contracts, insurance policies, and futures. The instrument is simple; what you do with it can be sophisticated or reckless. A portfolio of 50 uncorrelated prediction market positions, sized with fractional Kelly, has more in common with a hedge fund than a casino.
They are not crystal balls. Market prices are probability estimates, not certainties. A contract at $0.80 still has a 20% chance of not happening. Prediction markets are the best probability aggregation mechanism we have — but they are not infallible, especially on thin or manipulated markets.
Prediction markets are the most structurally fair trading venue available for event outcomes. Low fees, no winner discrimination, multi-category coverage, transparent order books. But "fair structure" doesn't mean "easy money" — 80% of participants still lose, because they trade without a system.
The rest of this education series builds that system: risk management (201–203), alpha strategies (301–302), and complete system design (401). Start with the structure, then add the edge.