Definition
What is vig in sports betting?
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Definition
Vig (also "juice" or "overround") is the implied bookmaker margin baked into market prices — the amount by which the market's implied probabilities sum to more than 100%. A two-way market with 110/110 American odds carries about 4.5% vig.
Vig is the structural cost of betting through a book. A line at "true" probability would sum to 100%; the book's line sums to more, and the difference is the house edge. Sharp books (Pinnacle, Cloudbet) run low vig; recreational books (BetMGM, FanDuel) run higher vig. Stripping vig from a market gives you the book's implied "true" probability, which is what model-based bettors compare against their own estimate.
How to strip vig
For a two-way market at decimal odds o_a and o_b:
implied_a = 1 / o_a
implied_b = 1 / o_b
overround = implied_a + implied_b (sums to >1)
true_a = implied_a / overround
true_b = implied_b / overround
The vig percentage is overround − 1. A market summing to 1.045 carries 4.5% vig.
Why sharp books matter
A Pinnacle market at 2% vig is much closer to “true probability” than a recreational book at 8%. The Pinnacle close is the standard sharp operators measure against because it’s the cleanest available proxy for true price.