EV Calculator

Calculate expected value (EV) and Kelly Criterion bet sizing by comparing your estimated probability against the offered odds.

%
$
$
Set your estimated true probability and enter the offered odds to calculate expected value.

How Does Expected Value Work?

Expected value quantifies whether a bet is profitable in the long run. Set your estimated true probability, enter the odds being offered, and the calculator determines your edge, dollar EV per bet, and the Kelly-optimal bet size. A +EV bet does not guarantee a win on any single wager, but across hundreds of bets, +EV positions generate profit.

How to Find Your Edge

Your edge is the gap between what you believe the true probability is and what the market implies. If the Odds Reference dashboard shows Polymarket pricing an event at 40¢ (40% implied) but Kalshi prices the same event at 52¢ (52% implied), the consensus suggests the true probability falls somewhere in between. Betting the 40¢ side when you estimate 50% true probability gives you a 10% edge.

Kelly Criterion and Bankroll Management

The Kelly Criterion recommends the stake that maximizes long-term bankroll growth. Full Kelly is mathematically optimal but volatile. Most professional bettors use half-Kelly or quarter-Kelly to smooth out variance. Enter your bankroll to see dollar-amount Kelly suggestions. If Kelly recommends 0%, the bet is -EV at your probability estimate.

Frequently Asked Questions

What is expected value (EV) in betting?
Expected value is the average amount you expect to win or lose per bet over a large number of repetitions. Positive EV (+EV) means the bet is profitable long-term. Negative EV (-EV) means you lose money over time. EV equals (probability of winning times profit) minus (probability of losing times stake).
How do I calculate expected value?
EV = (True Probability x Net Profit if Win) - (Probability of Losing x Stake). For a +150 bet where you estimate 45% true probability: EV = (0.45 x $150) - (0.55 x $100) = $67.50 - $55.00 = +$12.50. This bet has a positive expected value of $12.50 per $100 wagered.
What does positive EV mean?
A positive EV (+EV) bet means your estimated true probability exceeds the implied probability from the odds. If you believe an outcome has a 55% chance but the odds imply 45%, you have a 10% edge. Over many bets at this edge, you expect to profit.
How do I estimate true probability?
True probability estimation combines research, statistical models, and market analysis. Compare odds across multiple platforms using the Odds Reference dashboard. If most sportsbooks price an outcome at -130 but one offers +110, the consensus implied probability suggests the +110 line may be +EV.
What is the Kelly Criterion?
The Kelly Criterion is a formula for optimal bet sizing given your edge. Kelly fraction = (edge) / (decimal odds - 1), where edge = true probability minus implied probability. It maximizes long-term bankroll growth but is aggressive. Most bettors use half-Kelly or quarter-Kelly to reduce variance.
What is the difference between EV and edge?
Edge is the percentage difference between your estimated true probability and the market implied probability. EV converts that edge into a dollar amount based on your stake size. An edge of 5% on a $100 bet yields +$5.00 EV. Same edge on a $1,000 bet yields +$50.00 EV.
Can prediction markets offer +EV opportunities?
Yes. Prediction markets are not perfectly efficient. Temporary mispricings, stale prices after news events, and low-liquidity markets can create +EV opportunities. The Odds Reference dashboard tracks prices across Polymarket, Kalshi, and other platforms so you can spot divergences.
Why does Kelly sometimes recommend no bet?
When your estimated true probability is lower than or equal to the implied probability, your edge is zero or negative. The Kelly Criterion correctly recommends a 0% allocation because there is no long-term profit to be made at those odds given your probability estimate.

Related Tools

Odds Converter Kelly Calculator Fee Calculator