Enter the two prices on a two-way market and this calculator removes the sportsbook fee, called the vig, to show the fair win chance and fair price for each side.
Example: a favorite at -150 and an underdog at +130 imply 60% and 43.5%, which add up to 103.5%. The extra 3.5 points are the fee. With the fee removed, the fair chances are about 58% and 42%.
Use the fair number to judge a bet. A price only has value when you think the side wins more often than its fair chance.