Gambling terms, explained straight

Odds, Probability & Bankroll

Odds vs probability formula

The odds vs probability formula converts a probability p into odds using odds = p/(1-p), and odds back into probability using p = odds/(odds+1).

Formula (probability to odds)
odds = p / (1 - p)12
Formula (odds to probability)
p = odds / (odds + 1)23
Range
Probability ranges from 0 to 1; odds range from 0 to +∞.2

Key points

  • Probability is the absolute chance of an event; odds compare the chance of the event to the chance of it not occurring.41
  • When probability is 0.5, odds are 1.0 (1 to 1).2
  • Betting odds are wagering prices, not the same as the mathematical odds-probability conversion.12

Where this term is used

Not the same as

  • Betting odds to probability — a method for converting a bookmaker's odds format into implied probability, whereas the odds vs probability formula is the general mathematical relationship between probability and odds

Sources

  1. Odds en.wikipedia.org Provides the odds formula and distinguishes betting odds from mathematical odds.
  2. 9.2 Binary logistic regression | R for Health Data Science argoshare.is.ed.ac.uk Supplies both conversion formulas and the range of probability and odds.
  3. [PDF] FEEG6017 lecture: Logistic regression southampton.ac.uk Confirms the odds-to-probability conversion formula.
  4. 3.10 Odds | Probability, statistics, and the likelihood ratio for non-experts [1st Edition] lrcfs-ap2.dundee.ac.uk Defines odds as a ratio and explains the conceptual difference from probability.

Sources are drawn from regulators, universities and published research, and each one is labelled with what it actually is — a preprint is not called a paper. Bookmaker and affiliate pages are never cited here, because a page that sells betting is not a neutral authority on it.