How Betting Odds Work
Every price a bookmaker offers is a statement about probability, wrapped in one of three formats.
The three odds formats
Decimal odds show your total return per $1 staked, including your original stake. Fractional odds show profit relative to stake - 5/1 means $5 profit for every $1 risked, on top of the stake back. Moneyline odds are shown as a positive or negative number relative to a $100 stake: +150 means $150 profit on $100, while -150 means you must stake $150 to profit $100.
What odds imply about probability
Every odds format converts into an implied probability - the win rate the price is built on. For decimal odds, that conversion is 100 divided by odds. This lets you compare a bookmaker's price against your own view of how likely an outcome really is.
Worked example
Odds of 2.50 imply 100 / 2.50 = 40% probability. A $20 stake at those odds returns $50 total if it wins - $30 profit plus the $20 stake back.
FAQ
Which odds format is best?
None - they're the same information in different clothes. Pick whichever your market displays and convert mentally, or use the Odds Converter.
Do implied probabilities from all outcomes add up to 100%?
No - they normally add up to slightly more than 100%. That extra is the bookmaker's margin.