Expected Value Calculator
Quantify your edge on any Polymarket or Kalshi market. Enter the current price and your estimated probability. Get the expected value per dollar, so you only take bets with real positive edge.
Formula for a YES bet: EV per $1 = (your_prob / price) - 1. Positive is profitable in expectation; negative is a losing bet.
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Expected Value FAQ
- What is Expected Value in prediction markets?
- Expected Value (EV) is the average return per dollar if you could place the same bet infinitely many times. It is computed as (your probability × payout) minus (probability of loss × stake). Positive EV means the bet makes money in expectation; negative EV means it loses money in expectation.
- How do I compute EV on Polymarket or Kalshi?
- Enter the current market price (e.g. 45 cents for a YES share) and your estimated true probability (e.g. 0.55 or 55%). The calculator shows your expected profit per dollar staked. EV per dollar = (your prob / price) - 1 for a YES buy. If that number is positive, take the bet; if negative, skip or consider buying NO.
- What counts as a meaningful edge?
- Professionals typically require at least 3 to 5 cents of edge (price difference vs. true probability) before placing a bet, to cover fees, slippage, and estimation error. A 1-cent edge on Polymarket is generally noise.
- Should I use EV or Kelly?
- EV tells you whether a bet is worth taking at all; Kelly tells you how much to size it. Use EV as the filter: only bets with meaningfully positive EV make the shortlist. Then use Kelly to decide the bet size. Both tools are free on this site.
- Why does the calculator show EV per dollar instead of total EV?
- EV per dollar is platform-independent and lets you compare bets of different sizes fairly. A bet with 10% EV per dollar is twice as good as one with 5% EV per dollar, regardless of stake. Once you know the per-dollar edge, Kelly determines how many dollars to commit.
Worked example
A Polymarket YES share trades at 40¢. You estimate the true probability at 55%.
EV per dollar: (0.55 / 0.40) - 1 = 0.375, or 37.5% expected return.
If you size the bet at $100, expected profit is $37.50. With Kelly sizing at 25% of a $1,000 bankroll, you would stake $250 with expected profit of $93.75.
If the same market traded at 60¢ instead, your EV would be negative (0.55 / 0.60 - 1 = -0.083) and you should skip or consider NO.