What is Vigorish (Vig) or Bookmaker Margin?

Definition: Vigorish, or vig, is the commission a sportsbook builds into its odds. In Europe the same concept is called bookmaker margin or overround.

How to calculate it:

Convert each outcome's odds into implied probability (1 / decimal odds).
Add up all outcomes in the market.
The amount above 100% is the margin.

Example: a two-way market priced at 1.91 / 1.91 (American -110 / -110) adds up to about 104.7%, so the margin is about 4.7%.

What affects the margin:

Market type: margins differ between main markets and specials.
Pre-match or live: live prices often include extra margin for latency risk.
Accumulators: margins multiply across selections.

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