Gambling terms, explained straight

Odds, Probability & Bankroll

Decimal odds to probability

Converting decimal odds to probability means working out the implied chance of an outcome by dividing 1 by the decimal number shown on the odds board.

Formula
p = 1 / D, where D is decimal odds12
Example
Decimal odds of 5.00 give a probability of 0.20 (20%)12
Even odds
Decimal odds of 2.00 map to a 50% implied probability13

Key points

  • Divide 1 by the decimal odds to get the implied probability; for odds of 4.00, the probability is 0.25 (25%).12
  • The result is an implied probability from the price, not necessarily the true chance, because bookmaker margin inflates the figure.4
  • This conversion applies to fixed-odds betting and betting exchanges that use decimal odds.14

Where this term is used

Odds & probability Odds vs probability Explains the difference between odds as a ratio of outcomes and probability as a proportion. Odds & probability Fractional odds to decimal Shows how to convert fractional odds into decimal format before calculating probability. Odds & probability Decimal odds to American Covers the conversion between decimal and American moneyline odds. Odds & probability Betting odds to probability A general guide to converting any odds format into implied probability. Odds & probability Odds vs probability formula Details the mathematical relationship between odds and probability. Odds & probability Odds vs probability in statistics Explains the statistical distinction between odds and probability in research contexts.

Sources

  1. Odds en.wikipedia.org Provides the core formula p = 1/D and the example of 5.00 odds equalling 20% probability.
  2. Inferring Tennis Match Progress from In-Play Betting Odds doc.ic.ac.uk Reinforces the reciprocal formula and the example conversion.
  3. 3.10 Odds | Probability, statistics, and the likelihood ratio for non-experts [1st Edition] lrcfs-ap2.dundee.ac.uk Confirms that even odds of 2.00 correspond to a 50% implied probability.
  4. Fixed-odds betting en.wikipedia.org Explains that implied probability from odds includes bookmaker margin, not true chance.

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.

Written and maintained by Ellis Warrender, writer and maintainer.

Last updated 28 July 2026. Spotted an error? Tell me and it gets fixed and logged on the corrections page.