How expected value works
EV = (win probability × profit if win) − (loss probability × stake)
Example
You can bet $100 at +120, and the fair no-vig price is +105 (a 48.78% win probability). The bet's expected value is $7.32, or 7.32% of your stake. Get the fair price from the no-vig calculator, then size the bet with the Kelly calculator.
FAQ
What is positive EV betting?
A positive EV (+EV) bet is one where the price you get pays more than the true chance of winning justifies. Over many such bets, results tend toward the expected value, though any single bet can lose.
How do I find the true win probability?
The usual approach is to take a sharp sportsbook's line, remove the vig with the no-vig calculator, and use the fair probability. Comparing that against softer books is how +EV tools find bets.
What's a good EV percentage?
Small edges are normal. Many +EV bettors take bets in the low single digits, because prices with large apparent edges are often stale or wrong.