Reading decimal odds
Decimal odds show the total return per unit, including the original unit. At 2.50, one unit would produce a total return of 2.50 units if the selection settled as a winner, meaning 1.50 units of profit before any tax or account-specific deduction.
The implied probability formula is 1 divided by the decimal price. Decimal odds are convenient for comparison because the same calculation applies whether a price is short or long.
Reading fractional odds
Fractional odds such as 3/2 show potential profit relative to the stake. Three units of potential profit are shown for every two units staked. Add one after dividing the numerator by the denominator to convert the fraction to decimal odds.
Even-money is often written as 1/1 and corresponds to decimal 2.00. Do not confuse the displayed profit fraction with total return.
Reading positive and negative American odds
Positive American odds show potential profit on a 100-unit stake. +150 corresponds to decimal 2.50. Negative odds show the theoretical stake required to make 100 units of profit; -200 corresponds to decimal 1.50.
American odds can look dramatically different around zero, so converting them before comparing operators is safer than judging the size of the number.
Conversion does not create value
Changing the display format does not change the price. Decimal 2.50, fractional 3/2 and American +150 describe the same pre-margin implied probability.
Check settlement terms, currency, market scope and operator licensing as carefully as the displayed number. A converted price is still attached to an uncertain event.