Polymarket prices look different from anything you've seen at a traditional sportsbook. There are no plus signs, no minus signs, no decimal odds. Instead, you see prices like $0.67 or $0.23. Once you understand the system, it's actually more intuitive than Vegas lines — here's the complete breakdown.
The Core Concept: Price = Probability
Every Polymarket contract pays $1.00 if it wins and $0.00 if it loses. The price you pay to buy a share is the market's implied probability that the outcome will occur. That's the entire system.
If you buy a share at $0.40 and the outcome occurs, you receive $1.00 — a profit of $0.60 per share. If it doesn't, your share expires at $0.00 and you lose the $0.40 you paid. The math is clean and linear, which is why Polymarket attracts traders who prefer probability-native formats over the vig-embedded confusion of traditional odds.
Binary Markets (Yes/No)
The simplest Polymarket format is a binary yes/no question. "Will the Fed cut rates in June?" — you buy YES or NO. The two sides should always sum to approximately $1.00 (small gaps can exist due to liquidity).
YES: $0.38 · NO: $0.62
The market thinks there's a 38% chance the Fed cuts in June and a 62% chance they hold. You believe the cut is more likely — say 55% — so you buy YES at $0.38, giving yourself a positive expected value edge.
Multi-Outcome (Categorical) Markets
Many Polymarket markets have more than two outcomes — think election nominees, award show winners, or price-bucket markets. Each possible outcome has its own share price. All prices should sum to approximately $1.00.
If you believe Spain's true probability is closer to 22% than 15%, you're looking at a mispriced market. Buying Spain at $0.15 and having it win pays $1.00 — a $0.85 profit per share. That potential edge is what Polymarket trading is fundamentally about.
Converting to American Odds
If you're more comfortable with Vegas-style odds, here's how to convert. Polymarket actually shows American odds as an option in its interface, but knowing the conversion manually is useful:
| Polymarket Price | Implied Probability | American Odds (approx) |
|---|---|---|
| $0.90 | 90% | -900 |
| $0.75 | 75% | -300 |
| $0.60 | 60% | -150 |
| $0.50 | 50% | +100 (even) |
| $0.33 | 33% | +200 |
| $0.20 | 20% | +400 |
| $0.10 | 10% | +900 |
| $0.05 | 5% | +1900 |
For favorites (price above $0.50): American odds = -(price / (1 - price)) × 100
For underdogs (price below $0.50): American odds = +((1 - price) / price) × 100
How to Calculate Expected Value
Expected value (EV) is the core concept for profitable prediction market trading. It answers the question: "Given my estimate of the true probability, is this price worth buying at?"
Positive EV means the market is underpricing the probability relative to your estimate. Negative EV means the market is overpricing it — pass or consider the NO side.
Polymarket vs. Vegas Lines
When the same event has both a Polymarket and sportsbook market — an NFL game, for example — comparing the two is a powerful consistency check. Significant divergence can signal a genuine edge in one of them.
- Polymarket tends to be faster. News breaks and Polymarket prices move within minutes because traders are watching constantly. Sportsbook lines often lag.
- Sportsbook lines have vig embedded. A -110 line on both sides of an NFL spread implies 52.4% for each side — that's the house edge built in. Polymarket has no comparable structural vig.
- Polymarket covers more. No sportsbook offers markets on Fed rate decisions, Oscar winners, or tech IPOs. Polymarket does.
- Liquidity differs by category. High-profile elections have deep Polymarket liquidity. Niche markets can be thin — meaning large trades move the price significantly.
Reading the Price History
Every Polymarket market shows a price chart of how the probability has moved over time. Reading this well is a genuine edge:
- A sharp spike on a specific date usually means breaking news hit — find out what it was
- A slow grind toward 90%+ is a market near consensus — low edge, but possibly still tradeable on the NO side if you disagree
- A price that snapped down and recovered often signals overreaction to news that turned out to be less significant than feared
- Flat price history on a high-stakes market means low trader interest — worth examining why
Common Beginner Mistakes
- Confusing price with value. A $0.05 market isn't automatically worth buying just because the payout would be +$0.95. It's only worth buying if you think the true probability is above 5%.
- Ignoring liquidity. A market with $200 total volume can be moved by a single $50 trade. Thin markets distort prices.
- Anchoring to recent price. A market that was $0.70 yesterday and is $0.45 today isn't automatically cheap — the news that moved it may be correct.
- Buying near-certain outcomes. Paying $0.95 for a share that wins at $1.00 only makes $0.05. The risk/reward is rarely worth it unless you're very confident.