Odds and math
Expected value
Also called EV, +EV, plus EV
Expected value converts an edge into money. Multiply your win probability by the decimal odds and subtract one: a 55% chance at +110 gives 0.55 × 2.10 − 1 = +0.155, or about 15.5 cents of profit per dollar over the long run.
Positive EV means the price pays more than the outcome deserves. It says nothing about any individual bet — a +EV wager loses constantly, and a −EV wager wins often enough to feel like genius.
The catch is that EV depends entirely on your probability estimate being right. A number derived from a small sample or a hunch produces confident-looking EV that means nothing. Being disciplined about where the probability comes from matters more than the arithmetic.
Want the full version? Read the in-depth guide, with worked examples and the math.
See also
- Edge — The gap between your estimated probability and the probability the price implies. Positive means value.
- Kelly criterion — A staking formula that sizes each bet to the size of its edge, maximising long-run bankroll growth.
- Value bet — A bet whose price is better than the true probability of the outcome.
- Variance — The spread of outcomes around your expected result — why good bettors have terrible months.