DomVsBeta

Glossary · Math

Expected Value (EV)

The average profit (or loss) per unit staked if the same bet were repeated infinitely.

EV is the only number that matters in the long run. A bet with positive EV (+EV) makes money over enough repetitions; a -EV bet loses money. Individual results are noise — EV is the signal.

Formula
EV per 1 unit staked = p · (d - 1) - (1 - p)
  p = your probability the bet wins
  d = decimal odds

Or as a percentage:
  EV% = (p · d - 1) · 100
Worked example
Odds 2.10, your probability 52%:
  EV% = (0.52 · 2.10 - 1) · 100 = +9.2%
On a $100 stake, expected profit is $9.20 per bet on average.
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