Expected value (EV) calculator
Enter a price and your honest estimate of the true win probability. We show the expected value per dollar, your edge over the line, and the Kelly stake the edge supports.
- EV per $1 staked
- —
- Edge
- —
- Recommended Kelly stake
- —
- Decimal odds
- —
- Break-even probability (from odds)
- —
- Expected value on your stake
- —
Why expected value is the only number that matters
Every price implies a break-even win rate. If you can win more often than that rate, the bet is +EV and will profit over a large enough sample; if you can’t, it’s -EV no matter how good the result feels on the day. Expected value collapses odds and probability into a single figure — the average return per dollar — so you can compare any two bets on the same scale.
The catch is that EV depends entirely on your probability estimate. The cleanest source is the no-vig fair price from a sharp market: use the vig & hold calculator to strip the margin out, then feed that probability in here. Once you know your edge, size the bet sensibly with the Kelly calculator.
Frequently asked questions
- What is expected value (EV) in betting?
- Expected value is the average profit or loss a bet would return if you could place it over and over. It equals your win probability times the decimal odds, minus one, per dollar staked. A positive number means the price is in your favour long term; a negative number means the book’s line is better than your estimate.
- What makes a bet +EV?
- A bet is +EV when your estimated true probability of winning is higher than the break-even probability baked into the odds. For example, +120 odds imply a 45.5% break-even; if you genuinely believe the outcome is 50% likely, the bet carries positive expected value. Finding and betting +EV consistently is the entire basis of long-term profit.
- How do I estimate the true probability of an outcome?
- The most reliable shortcut is to take the no-vig fair probability from a sharp book — strip the margin out of both sides of the market and use that number as your baseline. You can also build your own model. Either way, the EV here is only as good as your probability input, so be honest and conservative with it.
- How is the recommended Kelly stake calculated?
- The Kelly criterion sizes your bet in proportion to your edge: stake = (probability × decimal − 1) ÷ (decimal − 1) of your bankroll. This calculator shows the full-Kelly percentage. Most bettors use a fraction of it — a quarter or a half — to smooth out variance, which you can model on the Kelly calculator.
For informational purposes only. Not betting or financial advice. Please gamble responsibly. 21+ where applicable.