EV Calculator
Enter the market price and your probability estimate. Get edge %, signal, and interpretation — instantly.
FOUNDATIONAL
Expected Value — Is this bet actually good?
What is this?
EV = Expected Value. It answers one question: "If I made this exact bet 100 times, would I make money or lose it?"
A positive EV bet makes money over time even if you lose today. A negative EV bet loses money over time even if you win today. Every casino game has negative EV for you. The goal is to only take positive EV positions — this tool tells you which side of that line you're on.
Real-World Example
→ The Scenario
Polymarket says there's a 55% chance Spain wins Group H. You buy YES at 55¢. But your research says Spain's real probability of winning their group is 72% (easier draw than people think).
EV = (0.72 × 45¢ profit) – (0.28 × 55¢ loss) = 32.4¢ – 15.4¢ = +17¢ EV per dollar
✅Action: +EV means bet it. +17¢ on a dollar is a strong edge. Size it proportionally.
Bottom line: If the EV number is negative, walk away. Doesn't matter how good it feels.
Full guide →Worked Example
Edge = (35% − 28%) / 28% = +25.0% edge. Market is pricing this 7pp below your model.
Interactive Calculator
The current YES price on Kalshi or Polymarket
Your model's estimate — not the market price
Formula: edge = (your probability − market price) / market price × 100
Related Tools
What is Expected Value in Prediction Markets?
Expected Value is the single most important concept in prediction market trading. It answers the question: is the market price wrong enough that I should take a position? If the market says a recession has a 28% chance and your model says 40%, that gap is your edge. But the size of the gap relative to the market price is what actually matters — a 12-point gap at 28¢ is a much larger edge than a 12-point gap at 70¢.
The formula normalizes the gap to the market price, giving you a clean edge percentage. A +25% edgemeans the market is underpricing the event by 25% relative to what you believe is fair value. That's the number that tells you whether to trade — and how confident to be when you do.
When to BUY, SELL, or SKIP
The ±5% threshold filters out noise. Markets are rarely perfectly efficient, but small gaps often close before you can act on them. A BUY signal at +5% means you have meaningful edge. A BUY signal at +20% means the market is significantly mispriced — size accordingly (see the Kelly Criterion calculator for position sizing).
A SELL signal means the market is overpricing the YES outcome relative to your estimate. If you already hold YES contracts, this is a signal to exit. If you don't hold a position, you can consider buying NO — which on Kalshi is simply the inverse of the YES price.
EV vs. the market price
This is different from asking “is the market price low?” A market at 10¢ might be a terrible trade if you think it should be at 8¢. A market at 80¢ might be the trade of the week if you think it should be at 95¢. EV is always relative to your probability estimate — which is why the estimate matters more than anything else. Sharpen your model, and the calculator tells you exactly when to act.
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