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How sports betting odds work
Odds are prices. This guide explains the three formats, how a price implies a probability, and where the sportsbook's margin hides.
Three ways to write the same price
American odds (the usual format in US sportsbooks): a plus number is the profit on a $100 wager; a minus number is the wager needed to profit $100. So +150 means a $100 wager profits $150 if it wins, and -110 means you wager $110 to profit $100.
Decimal odds show total return per $1 wagered, wager included. +150 is 2.50; -110 is 1.9091.
Fractional odds show profit over wager: +150 is 3/2; -110 is 10/11.
Convert any price with the odds converter.
From a price to an implied probability
Implied probability is 1 divided by the decimal odds. -110 is 52.38%; +150 is 40.00%; -200 is 66.67%. It is the probability the price "asks you to believe" in order to break even on average. It is not a forecast, and it is not the true chance of anything.
Where the sportsbook's margin hides
In a two-way market priced -110 on both sides, each side implies 52.38%, so the two add to 104.76%. The extra 4.76% is the margin, often called the vig or juice. Restated as a share of money wagered (the "hold"), it is 4.55%. A sportsbook that takes balanced wagers on both sides keeps about that share on average, regardless of who wins. The vig calculator does this for any prices.