Expected Value Calculator
Calculate the expected value of a Polymarket trade. Set the market price and your estimated true probability to see whether a trade is +EV, your edge in percentage points, and how sensitive your EV is to estimation error.
Total EV
+$19.00
EV per Share
+$0.10
Edge
+10.0%
Sensitivity Analysis
How your EV changes if your true probability estimate is off
| Your True Probability | EV per Share | Total EV |
|---|---|---|
| 45.0%(-15pp) | -$0.06 | -$11.00 |
| 50.0%(-10pp) | -$0.01 | -$1.00 |
| 55.0%(-5pp) | +$0.05 | +$9.00 |
| 60.0%(your estimate) | +$0.10 | +$19.00 |
| 65.0%(+5pp) | +$0.14 | +$29.00 |
| 70.0%(+10pp) | +$0.20 | +$39.00 |
| 75.0%(+15pp) | +$0.24 | +$49.00 |
EV = (true probability × shares) − stake − fee. Fee formula: fee = shares × price × 0.04 × (p(1-p))^1. Maker orders pay zero fees.
What Is Expected Value?
Expected value (EV) is the average profit or loss you would expect if you repeated a trade many times under the same conditions. A positive EV trade means you expect to profit over time; a negative EV trade means you expect to lose. The goal of serious prediction market trading is to consistently find and exploit +EV opportunities.
EV depends on three factors: the cost of entering the trade (the market price plus fees), the potential payout ($1.00 per share if correct), and the true probability of the outcome occurring. The market price reflects the crowd’s estimate of the probability. If your estimate is more accurate, the difference is your edge.
Why the Sensitivity Table Matters
Nobody estimates probabilities perfectly. The sensitivity table shows what happens to your EV if your probability estimate is off by 5, 10, or 15 percentage points. A trade that looks +EV at your estimate may turn negative if you are even slightly wrong — this is especially true when your edge is thin. Use the table to assess how confident you need to be before committing capital.
Frequently Asked Questions
What is expected value in prediction markets?
EV = (true probability × payout) - cost - fees. If you believe an outcome has a 65% chance but the market prices it at 50%, your EV per share is roughly $0.15 minus fees. For a deeper dive, see our fundamental analysis strategy.
What is edge in prediction market trading?
Edge is the difference between your estimated true probability and the market’s implied probability. Larger edges mean higher EV — but only if your estimate is accurate. See our quantitative analysis guide for methods to estimate probabilities more rigorously.
How accurate do my probability estimates need to be?
Check the sensitivity table in the calculator. If your EV turns negative when your estimate is off by just 5 points, the trade is fragile. Robust +EV trades remain positive even with moderate estimation error.
Size your positions based on your edge using the Kelly Criterion calculator. Calculate exact fees with the fee calculator, or check your P&L with the profit calculator.