Glossary / Betting math / Vig
A ParlayAPI glossary entry

Vig (Juice)

The vig (short for vigorish, also called juice) is the bookmaker's commission embedded in the prices of a market. Mathematically it is the amount by which the sum of the market's implied probabilities exceeds 1.0 - the reason both sides of a coin-flip market are -110 instead of +100.

Worked example

# Standard US two-way pricing
        -110 / -110  ->  52.38% + 52.38%  =  104.76% implied sum
        vig  =  4.76%   # the book's margin over a fair 100%
        # A reduced-juice -105/-105 market carries only ~2.44% vig

The vig is why breaking even at -110 requires a 52.38% win rate, not 50%. Serious bettors treat the vig as the cost of doing business and reduce it two ways: shopping lines across books, and betting into low-vig markets.

Where it shows up in ParlayAPI

Because ParlayAPI returns every book's prices side by side for the same market, you can compute per-book vig directly from one odds response - sum the implied probabilities of the two sides and subtract 1.0. The +EV scanner and arb scanner both do this continuously via devigging.

Related terms

OverroundHow far implied probabilities sum past 100%. HoldThe book's expected margin on a market. DeviggingStrip the bookmaker margin to a fair probability. No-vig priceA price with the book's margin stripped out.