Product
Betting Odds
Definition
The price of a bet, expressing the payout on a winning stake and implying the probability the price-setter assigns to the outcome. Displayed in decimal, fractional or American format, all three convertible, and always incorporating the bookmaker’s margin so that implied probabilities across a market sum to more than 100 per cent.
Key takeaways
- Odds are the price of a bet in decimal, fractional or American format; all convert through the decimal form.
- Implied probability is 1 divided by decimal odds, and a market’s implied probabilities sum to more than 100 per cent; the excess is the overround.
- Prices open from a model, move with information, money and the sharp market, and close at the market’s consensus.
- Headline markets are priced thin for volume; multiples and props carry the margin.
Why it matters
Odds are the sportsbook's product, and reading them is the industry's basic literacy. Decimal odds state total return per unit staked (3.50 returns 3.50 for 1, stake included); fractional odds state profit relative to stake (5/2 wins 5 for 2); American odds state profit on 100 for positive prices (+250) and the stake needed to win 100 for negative ones (minus 200). All three describe the same price and convert to each other through the decimal form. The implied probability is one divided by the decimal odds, and it is always higher than the bookmaker's true estimate because the margin is built in: the implied probabilities across a two- or three-way market sum to 103 to 110 per cent, and the excess is the overround.
Where odds come from is the trading function's work. An opening price is the compiler's or the model's estimate plus margin; it then moves with information (team news, injuries), with money (the book shortens what is being backed and lengthens the rest) and with the sharp market (the prices of the exchanges and the bookmakers that take the largest informed bets). The closing price is the market's consensus and the benchmark against which both bettors and traders are judged.
For the business, odds are the lever of margin and volume together. Competitive prices on the headline markets bring customers in at thin margins; the wider margins on multiples, props and less liquid markets earn the money. Regulators are interested in odds for fairness (bets honoured, palpable errors handled consistently) and for marketing (boosted odds are promotions), and in the United States the display format and the rules of settlement are part of state regulation.
Frequently asked questions
How do you convert fractional odds to decimal?
Divide the fraction and add 1. 5/2 is 2.5 plus 1, or 3.50; 1/2 is 0.5 plus 1, or 1.50. To get American odds from decimal, for prices above 2.00 multiply (decimal minus 1) by 100; for prices below 2.00 divide minus 100 by (decimal minus 1).
What does it mean when odds are "odds-on"?
That the outcome is priced as more likely than not: decimal odds below 2.00, fractional odds with the larger number second (such as 1/2), or negative American odds. The payout is less than the stake.
Why do odds differ between bookmakers?
Because each sets its own margin, holds its own liabilities and forms its own view, and because prices move at different speeds. Comparing prices across bookmakers is called line shopping and is the first habit of a serious bettor.