Prediction Markets Surge Past $1B: Calculate Your Edge
Polymarket volumes surged past $1 billion in 2026 as prediction markets gained mainstream traction for betting on elections, recessions, crypto prices, and geopolitical events. Unlike stocks, these are zero-sum games — one person's gain is another's loss. The key to profitability is finding positive expected value: when your assessed probability exceeds the market's implied probability. This calculator helps you quantify your edge, optimal bet size (Kelly Criterion), and expected ROI before placing a bet on Polymarket, Kalshi, or similar platforms.
About This Calculator: Prediction Market ROI
Why: With prediction markets exploding in popularity, users need to understand whether a bet has positive expected value before risking capital. Most participants lose money because they bet without quantifying their edge. This calculator reveals the math: implied probability, your edge, expected ROI, and Kelly-optimal bet sizing.
How: Enter the contract price (e.g., 0.35 for 35¢), your estimated true probability, investment amount, platform fee, and hold duration. The calculator computes expected value, ROI, Kelly optimal bet size, potential profit/loss, and annualized return. Use the examples to explore different scenarios.
📋 Quick Examples — Click to Load
📊 Expected Value vs Risk
Expected value, potential profit if you win, and potential loss if you lose
📈 ROI at Different Probability Assessments
How ROI changes as your estimated probability varies (same contract price)
🍩 Probability Comparison: Implied vs Your Estimate
Market implied probability vs your assessed probability
📐 Kelly Optimal vs Actual Bet Sizing
Full Kelly optimal bet size vs your fractional Kelly bet
⚠️For educational and informational purposes only. Verify with a qualified professional.
Polymarket volumes surged past $1 billion in 2026 as prediction markets like Polymarket and Kalshi gained mainstream traction for betting on elections, recessions, crypto prices, and geopolitical events. Unlike stocks, these are zero-sum: one person's gain is another's loss. The key to profitability is finding positive expected value — when your assessed probability exceeds the market's implied probability. This calculator helps you quantify your edge, optimal bet size (Kelly Criterion), and expected ROI before placing a bet.
Sources: Polymarket, Kalshi, Metaculus, CFTC.
Key Takeaways
- • Edge = your probability minus implied probability. Positive edge is required for long-term profitability.
- • Expected value = (win prob × profit) − (loss prob × loss). Only bet when EV > 0.
- • Kelly Criterion tells you the optimal bet size; most traders use 25–50% of full Kelly to reduce variance.
- • Platform fees (e.g., Polymarket 2%) reduce profits — factor them into your EV calculation.
Did You Know?
How Does Prediction Market ROI Calculation Work?
Implied Probability and Edge
The contract price equals the market's implied probability. A 35¢ contract implies 35%. Your edge is your assessed probability minus implied: e.g., 55% − 35% = 20pp edge.
Expected Value Formula
EV = (trueProb × (1 − price) × investment) − ((1 − trueProb) × price × investment). If you win, you profit (1 − price) per dollar; if you lose, you lose the price. Multiply by your investment and probabilities.
Kelly Criterion
Kelly % = edge / odds, where odds = (1 − price) / price. For a 35¢ contract, odds = 0.65/0.35 ≈ 1.86. A 20pp edge gives Kelly ≈ 10.8%. Use fractional Kelly (e.g., 25%) to reduce risk.
Expert Tips
Prediction Market Platform Comparison
| Platform | Fee | Regulation | Focus |
|---|---|---|---|
| Polymarket | 2% on profits | CFTC no-action | Elections, crypto, macro |
| Kalshi | Variable | CFTC regulated | Events, economics |
| Metaculus | N/A (forecasting) | Non-trading | Long-term forecasts |
| PredictIt | 10% on profits | CFTC no-action | Elections, politics |
Frequently Asked Questions
What are prediction markets?
Prediction markets are platforms where participants buy and sell contracts tied to real-world events (elections, recessions, crypto prices). Each contract pays $1 if the event occurs and $0 otherwise. The market price represents the implied probability — a 35¢ contract implies a 35% chance. Polymarket and Kalshi have driven volumes past $1B as of 2026.
How do Polymarket contracts work?
Polymarket uses binary outcome markets: YES contracts pay $1 if the event happens, NO contracts pay $1 if it does not. Prices trade between $0.01 and $0.99. A 65¢ YES contract means the market believes a 65% chance. Polymarket charges a 2% fee on profits. Contracts settle based on designated resolution sources (e.g., official election results).
What is expected value?
Expected value (EV) is the average profit or loss per dollar invested if you repeated the bet many times. EV = (win probability × profit if win) − (loss probability × loss if lose). A positive EV means the bet is profitable in the long run. For a 35¢ contract where you assess 55% true probability: EV = 0.55 × $0.65 − 0.45 × $0.35 = $0.20 per $1 invested.
What is the Kelly Criterion?
The Kelly Criterion is a formula that determines the optimal bet size to maximize long-term growth. Kelly % = edge / odds, where edge is your probability minus implied probability, and odds = (1 − price) / price. Full Kelly is aggressive; most traders use 25–50% of Kelly (fractional Kelly) to reduce variance while preserving most of the growth benefit.
Are prediction markets legal?
In the US, Polymarket operates under CFTC no-action relief for event contracts. Kalshi is a CFTC-regulated designated contract market. Both are legal for US users. Overseas platforms vary by jurisdiction. Sports betting and election markets have different regulatory treatment — always verify your local laws before participating.
How accurate are prediction markets?
Academic research shows prediction markets often outperform polls, especially for elections. Metaculus and PredictIt have demonstrated strong calibration. However, thin markets can be manipulated, and sentiment can drift from fundamentals. Markets with high volume (e.g., presidential elections) tend to be more accurate than niche events.
Key Statistics
Official Data Sources
⚠️ Disclaimer: This calculator provides estimates for educational purposes. Prediction markets involve risk; you can lose your entire investment. Past performance does not guarantee future results. Verify platform fees and regulations in your jurisdiction. This is not financial or legal advice.