How Prediction Markets Work: A Complete Guide

Prediction markets are probability exchanges

A prediction market lets you buy and sell contracts on real-world outcomes. Each contract pays $1.00 if the event happens and $0.00 if it does not. The trading price is the market's consensus probability.

A contract at $0.65 means the market prices that outcome at 65% likely. You buy it for $0.65. If the event happens, you collect $1.00 and profit $0.35. If it does not happen, you lose your $0.65. That is the entire mechanism. No point spreads, no over/unders, no bookmaker setting lines. Just a price between $0.01 and $0.99 that moves as participants trade.

This structure makes prediction markets fundamentally different from sportsbooks. On a sportsbook, you bet against the house at odds the house sets. On a prediction market, you trade against other participants at prices the market determines. The platform takes a fee. The math still works the same way. Expected value is still the only number that matters.

Prediction markets cover territory that sportsbooks cannot touch: elections, economic data, Fed rate decisions, Supreme Court rulings, weather events, and tech launches. Anywhere there is an uncertain binary outcome, someone can build a contract around it. And because participant pools are smaller and less sophisticated than the sportsbook market, the pricing inefficiencies are larger and last longer.

Step 1Learn contract pricing

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Step 2Choose a platform

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Step 3Read the order book

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Step 4Estimate true probability

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Step 5Calculate edge after fees

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Step 6Size and execute the trade

How to read and interpret contract prices

Every prediction market contract has two sides: Yes and No. On a well-functioning market, the Yes price and the No price add up to approximately $1.00 (the small gap is the spread).

If "Will the Fed cut rates in March?" trades at Yes $0.40 / No $0.62, the market consensus is roughly 40% for a cut. The 2-cent gap ($0.40 + $0.62 = $1.02) represents the bid-ask spread, which is one of the costs you pay to trade.

Reading a price as implied probability. A Yes contract at $0.72 implies 72% probability. To convert this to American odds, use the formula for favorites: -100 x (price / (1 - price)) = -100 x (0.72 / 0.28) = -257. The market converter handles this in both directions instantly.

Worked example: two sides of one market. A Kalshi contract on "Will inflation exceed 3% in Q1?" shows Yes at $0.35 and No at $0.66.

• Yes implies 35% probability. If you buy Yes at $0.35 and it resolves Yes, you profit $0.65.
• No implies 66% probability. If you buy No at $0.66 and it resolves No, you profit $0.34.
• The 1-cent gap ($0.35 + $0.66 = $1.01) is the spread cost.

If you believe true inflation probability exceeds 3% with 50% likelihood, the Yes contract at $0.35 represents a 15-cent edge before fees. That is a massive edge. Run it through the PM EV calculator to see the exact expected value.

Multi-outcome markets work the same way but with more contracts. "Which party wins the 2028 presidential election?" might have Democrat at $0.47, Republican at $0.49, and Other at $0.06. All contracts should sum to approximately $1.00. When they do not, there is either a spread cost or a pricing inefficiency. The multi-outcome calculator checks for mispriced contracts across all outcomes. For the full breakdown on trading these, read the multi-outcome markets guide.

The mechanics of buying and selling contracts

Prediction markets use order books, just like stock exchanges. Understanding order book mechanics is the difference between getting a fair price and overpaying.

Limit orders let you set your price. You submit "Buy 100 Yes contracts at $0.45." Your order sits on the book until someone sells at $0.45 or lower. You control your entry price, but the order might not fill.

Market orders fill immediately at whatever prices are available. You get instant execution but eat the spread. On a thin market, a market order for 500 contracts might fill the first 100 at $0.45, the next 200 at $0.47, and the last 200 at $0.50. Your average price is $0.474, not $0.45. The liquidity calculator simulates this slippage before you commit capital.

Selling before settlement is the structural edge prediction markets have over sportsbooks. You buy at $0.40. News breaks. The contract jumps to $0.70. You sell and pocket $0.30 per contract without waiting for the event to resolve. This ability to exit changes position management, risk control, and capital efficiency. Learn more about this in the event contract trading guide.

Worked example: a round-trip trade. You buy 200 Yes contracts on "Will GDP growth exceed 2%?" at $0.52 each. Total cost: $104.

Two weeks later, a strong jobs report pushes the contract to $0.68. You sell all 200 at $0.68. Revenue: $136. Profit: $32 (30.8% return in two weeks). You never waited for the GDP number. You traded the probability movement.

This is why bankroll turnover matters so much in prediction markets. Capturing $0.16 of movement in two weeks and redeploying that capital beats holding for a $0.48 payout in three months. Your capital works harder. The turnover calculator quantifies exactly how much faster your bankroll grows at higher turnover rates. For a complete framework on managing capital across positions, see the prediction market bankroll management guide.

Key platforms and how they differ

Four platforms dominate the prediction market landscape. Each has distinct fee structures, market selection, and user bases.

Kalshi is the only CFTC-regulated prediction market exchange in the US. It offers event contracts on economics, politics, weather, and an expanding set of sports events. Kalshi charges approximately 7% of profit on winning contracts held to settlement. No fee on losses, no fee on secondary market trades closed before settlement. This makes Kalshi cheaper for active traders who exit positions early, but expensive for high-priced contracts held to resolution. See the exact impact at any price point with the fee calculator.

Polymarket runs on blockchain (Polygon) and is the highest-liquidity prediction market for major events. It charges no explicit trading fee. Your cost is the bid-ask spread (typically 1-2 cents on liquid markets) plus crypto on/off-ramp costs. Polymarket consistently has the deepest order books on political events. The trade-off: it is not available to US-based traders.

DraftKings and Robinhood have entered the prediction market space, bringing mainstream audiences and increased liquidity. DraftKings integrates event contracts alongside its sportsbook, making cross-platform comparison trivially easy for existing users. Robinhood's prediction market product (through its Kalshi partnership) brings equity-trading UX to event contracts.

For a detailed comparison of the two most established platforms, read the Kalshi vs Polymarket comparison. For how prediction market costs stack up against sportsbook vig, the prediction market vs sportsbook comparison puts both systems side by side.

How fees affect your edge

Fees are the silent killer in prediction markets. A 10-cent edge on paper can shrink to 5 cents after platform costs. On thinner margins, fees flip +EV trades to -EV entirely.

The math behind fee drag. You find a contract at $0.55 on Kalshi. You believe the true probability is 65%. Your raw edge is 10 cents. But Kalshi takes 7% of your $0.45 profit if you win.

Pre-fee EV: (0.65 x $0.45) - (0.35 x $0.55) = $0.2925 - $0.1925 = +$0.10

Post-fee EV: (0.65 x $0.45 x 0.93) - (0.35 x $0.55) = $0.272 - $0.1925 = +$0.0795

Fees cut your edge by 20.5%. On a 3-cent edge, fees could eliminate your profit entirely.

The practical rule: your estimated edge should be at least 3 times the fee drag. This 3x buffer accounts for estimation error in your probability assessment. The break-even calculator shows exactly how much edge you need at any contract price to clear zero after fees. The full breakdown of fee structures, worked examples, and platform-specific strategies is in the prediction market fees guide.

Fee awareness also determines which platform to use. On contracts above $0.70, Kalshi's winner-pays model becomes expensive. On illiquid markets, Polymarket's spread cost can exceed Kalshi's percentage fee. Always compare the effective cost on both platforms before routing a trade. The fee calculator runs the comparison automatically.

Finding edge: the math behind profitable prediction market trading

The core question in any market is the same: is the price wrong? In prediction markets, that means asking whether the contract price diverges from the true probability of the event. If it does, and the gap survives fees, you have edge.

Step 1: Estimate true probability. This is the hard part. Sources include your own research, domain expertise, statistical models, or sharp market prices on the same event. If Polymarket prices an election outcome at $0.52 and Kalshi prices it at $0.48, at least one market is mispriced. The question is which one, or whether the truth is somewhere in between.

Step 2: Calculate expected value after fees. Use the PM EV calculator to get the exact number. Input the contract price, your probability estimate, and the platform. The calculator shows pre-fee EV, post-fee EV, and the Kelly-optimal position size.

Step 3: Size the position. Position sizing in prediction markets follows the same Kelly framework as sports betting. The Kelly Criterion gives the optimal fraction of your bankroll to risk. Most traders use half Kelly or quarter Kelly to reduce variance. Run the numbers through the Kelly calculator.

Worked example: finding and sizing a trade. A Kalshi contract asks "Will the unemployment rate exceed 4.5% in March?" It trades at $0.30. Your model, based on leading economic indicators, estimates 42% probability.

Raw edge: $0.42 - $0.30 = $0.12 (12 cents)

Post-fee EV: (0.42 x $0.70 x 0.93) - (0.58 x $0.30) = $0.2734 - $0.174 = +$0.0994

Kelly %: Using decimal odds of 1 / 0.30 = 3.33 and p = 0.42:

Kelly = (0.42 x 3.33 - 1) / (3.33 - 1) = 0.398 / 2.33 = 17.1%

Half Kelly: 8.6% of bankroll.

On a $5,000 bankroll, that is $430 allocated to this position, or approximately 1,433 contracts at $0.30.

This pipeline works the same for every trade. Estimate probability. Calculate EV. Check that edge clears the 3x fee threshold. Size with Kelly. Execute. The PM EV calculator runs steps 2 and 3 together.

Cross-platform edge. When the same event trades on both a sportsbook and a prediction market, price discrepancies create arbitrage opportunities. Even when a pure arb does not exist, comparing prices across platforms improves your probability estimate. If a sportsbook implies 58% on a de-vigged line and a prediction market prices the same outcome at 52%, someone is wrong by 6%. The arbitrage calculator checks whether you can profit from both sides simultaneously.

Understanding how event contracts compare to traditional options also helps frame the risk profile. And if you are wondering about the legal and regulatory landscape, the prediction markets vs gambling analysis covers where the line sits.

Prediction markets also create opportunities for correlated positions across related contracts. If you hold positions in both "Will the Fed cut rates?" and "Will the S&P 500 hit a new high?" those outcomes are correlated. The position risk calculator shows how correlated holdings amplify your portfolio risk.

Building your prediction market strategy

The concepts in this guide connect as a system. Pricing tells you what the market believes. Fee math tells you what it costs to trade. EV math tells you whether the trade is worth taking. Position sizing tells you how much to risk. And bankroll management keeps you in the game long enough for the math to converge.

Every spoke in this system has a deeper guide:

• Trading mechanics: How to Trade Event Contracts
• Position sizing: Prediction Market Position Sizing
• Bankroll management: Prediction Market Bankroll Management
• Fee optimization: Prediction Market Fees Explained
• Platform selection: Kalshi vs Polymarket and Sportsbook vs Prediction Market
• Advanced strategy: Prediction Market Strategy

The tools exist to make each step faster. The market converter translates prices. The fee calculator quantifies costs. The PM EV calculator finds edge. The Kelly calculator sizes positions. Run the numbers before every trade. That is the entire strategy.

Frequently asked questions

How do prediction markets work?

Prediction markets let you buy and sell contracts that pay $1 if an event happens and $0 if it does not. The contract price equals the market's implied probability. You profit when you buy contracts priced below the true probability of the event.

What is a prediction market contract?

A prediction market contract is a binary instrument that resolves to $1.00 (Yes) or $0.00 (No) based on a real-world outcome. Buying a Yes contract at $0.40 means you pay $0.40 and collect $1.00 if the event occurs, profiting $0.60.

Are prediction markets legal in the US?

Kalshi is the only CFTC-regulated prediction market exchange operating in the US. It offers legal event contracts on economics, politics, weather, and sports. Polymarket is not available to US residents. DraftKings and Robinhood also offer event contracts through regulated channels.

How much money can you make on prediction markets?

Profitability depends on your edge and bankroll. A trader with a consistent 5% edge, half-Kelly sizing, and high turnover can generate 15-30% annual returns on their bankroll. Most casual participants lose money because they trade without calculating expected value.

What is the difference between prediction markets and sports betting?

Prediction markets use order books where you trade contracts against other participants. Sportsbooks set fixed odds and you bet against the house. Prediction markets cover non-sports events (politics, economics), allow you to sell positions before settlement, and often have lower fees than sportsbook vig.