Understanding Prediction Market Odds

Prices as Probabilities

The most important thing to understand about prediction markets is that prices represent probabilities. A share priced at $0.73 represents a 73% implied probability. This is fundamentally different from sports betting, where odds are quoted in various confusing formats (American, decimal, fractional).

Prediction markets are elegant: the price is the probability. No conversion needed.

How to Read a Market

Every Polymarket market has two sides: Yes and No. The prices are complementary, meaning they always sum to approximately $1.00. For example:

• Yes at $0.65 means 65% chance the event happens
• No at $0.35 means 35% chance it doesn't happen

When you see a market at 82%, the crowd believes there's an 82% probability of that outcome. But remember: the crowd isn't always right. Your edge comes from identifying when the market is wrong.

Expected Value

The key concept for profitable trading is expected value (EV). A bet has positive expected value when you believe the true probability is higher than the market price.

For example: A "Yes" share is priced at $0.40 (implied 40% chance). If you believe the true probability is 55%, your expected value per dollar invested is:

EV = (0.55 x $1.00) - (0.45 x $0.00) - $0.40 = +$0.15

This means you expect to make $0.15 profit per share over time. Positive EV bets are the foundation of profitable prediction market trading.

The Edge Concept

Your "edge" is the difference between the market's implied probability and your estimated true probability. Larger edges mean more profitable opportunities, but they're also rarer and can signal that you're missing information the market has.

• Small edge (1–5%): Common, low profit potential per trade, requires volume
• Medium edge (5–15%): Worth taking in liquid markets, good risk/reward
• Large edge (15%+): Rare and lucrative, but double-check your reasoning — the market might know something you don't

Comparing with Traditional Betting

If you're coming from sports betting, here's a quick conversion guide:

• Prediction market $0.50 = Even odds = +100 (American) = 2.00 (Decimal)
• Prediction market $0.25 = 3:1 against = +300 (American) = 4.00 (Decimal)
• Prediction market $0.80 = 4:1 favorite = -400 (American) = 1.25 (Decimal)

The advantage of prediction market format is its simplicity and direct connection to probability.

Market Efficiency

Prediction markets are reasonably efficient — meaning prices tend to reflect available information quickly. But they're not perfectly efficient, especially in:

• New markets: Fresh markets may take time to find the "correct" price
• Low-volume markets: Less participation means less information aggregation
• Fast-moving news: Markets sometimes lag behind breaking developments by minutes or hours
• Complex conditional probabilities: Markets can misprice events with many dependencies

These inefficiencies are where informed traders find their edge.