How Polymarket Odds Work: Understanding Prediction Market Prices

Price = Probability

On Polymarket, every outcome of a market is represented as a share that can be bought between 1¢ and 99¢. The price directly represents the market’s estimated probability of that outcome. If “Lakers win” trades at 65¢, the market collectively believes there’s a 65% chance the Lakers win.

Winning shares pay out exactly $1.00. Losing shares pay $0.00. Your profit on a winning trade is: $1.00 - entry_price. Your loss on a losing trade is your entry price.

For binary markets (Yes/No), the Yes price and No price always sum to approximately $1.00. If Yes is at 65¢, No is at 35¢. This is because buying $1 of Yes and $1 of No guarantees a $1 payout regardless of outcome — any deviation from $1 total would create a risk-free arbitrage.

The CLOB Order Book

Polymarket uses a CLOB (Central Limit Order Book), the same type of order book used by stock exchanges. Buyers place bids at prices they’re willing to pay. Sellers place asks at prices they’re willing to sell. When a bid meets an ask, a trade happens.

The “midpoint” price — halfway between the best bid and best ask — is what’s displayed as the market price. A spread of 1–2¢ is typical for liquid markets. Wider spreads (5¢+) indicate low liquidity or uncertainty.

Understanding the order book is important because large trades can “walk the book” — eating through multiple price levels. A $50K market buy might push the price from 55¢ to 60¢ by exhausting all asks between those levels. This is why whale trades move markets and why speed matters when following them.

Expected Value (EV)

Expected value is the concept that separates gamblers from traders. EV calculates the average profit per trade if you could repeat it many times.

Formula: EV = (probability_of_winning × profit_if_win) - (probability_of_losing × loss_if_lose)

Example: You buy at 55¢. You believe the true probability is 65%.

• Profit if win: $1.00 - $0.55 = $0.45
• Loss if lose: $0.55
• EV = (0.65 × $0.45) - (0.35 × $0.55) = $0.2925 - $0.1925 = +$0.10 per share

A positive EV of $0.10 means that over many such trades, you’d average 10¢ profit per share. This is the mathematical basis for profitable trading. Edge Radar’s daily picks calculate this for every candidate market using AI probability estimation.

Edge = Your Advantage

Edge is the gap between what you believe the true probability is and what the market price implies: edge = true_probability - market_price.

If you think an outcome has a 70% chance and the market prices it at 55¢, your edge is 15¢. The larger the edge, the more confident you should be in the trade.

Edge Radar’s daily picks assign confidence based on calculated edge:

How Prices Move

Prices change when new information enters the market or when large traders adjust their positions. Common catalysts:

• News events — Injury reports, policy announcements, economic data. Prices adjust within minutes.
• Whale trades — A $50K buy can move a market 3–5¢ instantly by eating through the order book.
• Time decay — As an event approaches, uncertainty decreases. Prices tend toward 0¢ or 100¢ as resolution nears.
• Sentiment shifts — Social media, poll data, or pundit opinions gradually shift retail positioning.

Smart money typically moves prices first. Retail follows later. This is why real-time whale alerts are valuable — they let you enter before the full price adjustment.

Polymarket Odds vs Sports Betting Odds

If you’re coming from traditional sports betting, here’s the translation:

The key difference: Polymarket has no vig. On DraftKings, a 50/50 market would price both sides at ~52.5¢ (-110 each), giving the house 5%. On Polymarket, both sides trade at 50¢ with no built-in margin.