How to Read Polymarket Odds and Find Value Bets

What Is a Polymarket Price?

Unlike traditional betting sites that show odds as +150 or 2.5x, Polymarket prices work differently. Every market outcome is priced between $0.00 and $1.00. This price directly equals the market's implied probability of that outcome occurring.

When you buy a share at $0.65 and the outcome resolves YES, you receive $1.00. If it resolves NO, you receive $0.00. Your potential payout multiplier is simply 1 divided by the price:

Implied Probability vs Real Probability

The core of prediction market edge is understanding the difference between what the market thinks will happen (implied probability) and what you think will actually happen (your estimated real probability).

The Math of Edge

Expected Value (EV) tells you whether a bet is profitable in the long run. The formula is straightforward:

That's a +17% expected return per dollar risked. Over many bets with consistent positive EV, you will profit — this is the mathematical foundation of profitable prediction market trading.

Types of Polymarket Markets

Binary Markets (Yes/No)

The most common type. One outcome wins, the other loses. UP/DOWN, YES/NO, ABOVE/BELOW. Prices of both sides always sum to approximately $1.00 (minus spread).

Categorical Markets (Multiple Outcomes)

Markets with 3+ outcomes — for example, "Who will win the election: Candidate A, B, or C?" Each outcome is priced separately. All prices sum to approximately $1.00.

Continuous / Range Markets

Markets asking where a value will land — e.g., "What will BTC price be on June 1st?" structured as multiple range outcomes. More complex, but also more opportunity for mispricing.

How to Spot a Value Bet

Finding edge requires a systematic approach. Here are the three most reliable methods:

Method 1: Base Rate Calibration

Look at historical rates for similar events. If central banks have cut rates in March 3 out of 10 times in similar economic conditions, the base rate is 30%. If the market shows 18%, you have edge.

Method 2: Information Asymmetry

You have information the market hasn't fully priced yet. A breaking news story, an earnings report you've analyzed more carefully than others, a geopolitical development with a precedent the crowd doesn't know.

Method 3: Model-Driven Edge

For structured markets like BTC 15-minute up/down, you can build a mathematical model (as we did at PolyLens) that computes the real probability based on observable data — BTC deviation, volatility, time remaining. When model probability diverges from market price by more than the fee threshold, you have a calculable edge.

Common Mistakes Beginners Make

• Betting on what they want to happen — not what will happen. Bias kills edge.
• Ignoring fees — 2% sounds small but can eliminate all edge on low-probability bets.
• Treating low prices as "cheap" — $0.02 is not cheap if the real probability is 0.5%.
• Overconfidence in single outcomes — markets aggregate thousands of people's views. Disagree carefully.
• Not tracking results — without records, you can't tell if your edge is real or luck.

Reading an Order Book

Polymarket uses a Central Limit Order Book (CLOB) model. You can see pending buy and sell orders at different prices. The bid-ask spread tells you the true cost of trading:

For liquid markets (BTC 15m, major political events), spreads are often $0.01–0.02. For illiquid niche markets, spreads can be $0.05–0.10, which means you need more edge to be profitable.

Position Sizing

Even with edge, sizing too large on any single bet can ruin you. The Kelly Criterion gives the mathematically optimal bet size:

In practice, most experienced traders use half-Kelly or quarter-Kelly to reduce variance. The math is right; the inputs are never perfect.