EV per Share
Total Expected Value
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Edge
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Kelly Fraction
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Verdict
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When Should You Use This?
Use this before every Polymarket trade. Enter YOUR probability estimate (not the market's) and the current share price. If the expected value is positive, the trade is worth taking over the long run. The Kelly fraction tells you how much of your bankroll to risk.
How It Works
1
Estimate Probability
Do your own research and estimate the true probability of the event. Be honest and calibrated. If you are unsure, you probably should not trade.
2
Enter Share Price
Input the current market price in cents. The difference between your probability and the market price is your edge.
3
Read the Verdict
Positive EV means the trade is profitable on average. The Kelly fraction tells you the optimal bet size. Most traders use half-Kelly or quarter-Kelly for safety.
Frequently Asked Questions
EV is the average outcome if you made the same bet thousands of times. Positive EV means you profit on average. It is calculated as: (Probability x Payout) - Cost.
The Kelly Criterion tells you the optimal fraction of your bankroll to bet to maximize long-term growth. Full Kelly is aggressive; most professionals use half-Kelly (bet half the recommended amount).
Research the event thoroughly. Look at historical base rates, expert opinions, polls, and competing prediction markets. Track your estimates over time to see if you are well-calibrated.
After accounting for fees (~1.5%), you need at least a 2-3% edge to be consistently profitable. Edges above 10% are rare but very profitable. Below 2%, transaction costs eat your edge.
Not always. Consider: (1) your confidence in the probability estimate, (2) the opportunity cost of capital, (3) correlation with your other positions, and (4) time until resolution.