Vig (vigorish)
The bookmaker's commission embedded in the odds, measured as the share of total stakes it keeps on a balanced market.
Vigorish (vig, or juice) is the bookmaker's commission. It is not charged as a fee: it sits inside prices that pay less than the fair odds on every outcome.
Calculation
For a two-way market with decimal odds a and b:
- Sum of implied probabilities: S = 1/a + 1/b.
- Vig = 1 minus 1/S.
Illustrative tennis market: 1.87 and 1.95.
- 1/1.87 = 0.5348; 1/1.95 = 0.5128; S = 1.0476.
- Vig = 1 minus 1/1.0476 = 4.54%.
Put differently: if stakes are balanced so the book pays the same whatever happens, it keeps 4.54% of the money taken.
Fair odds
Divide each implied probability by S: 0.5348/1.0476 = 51.05% and 48.95%. Fair odds are 1.959 and 2.043.
This proportional method is the simplest. Others, such as the power or Shin methods, shift more of the margin onto the longer price, reflecting the favourite-longshot bias.
Comparison
| Price both sides | Vig |
|---|---|
| 1.95 / 1.95 | 2.50% |
| 1.91 / 1.91 | 4.50% |
| 1.87 / 1.87 | 6.50% |
Lower is better for the bettor. See also overround.