Vig (overround), defined
The vig — also called the overround or margin — is the amount by which a market's implied probabilities exceed 100%.
, 3 min read
If the two sides of a match market imply 55% and 50%, the market sums to 105%. Those 5 percentage points are the vig. It is not a fee added on top; it is baked into every price, which is why reading odds naively overstates each outcome's chance. The word is short for vigorish, and bookmakers and exchanges rely on it as their built-in edge — the mathematics of bookmaking is essentially the study of how that margin is set and recovered.
Vig varies. Tighter markets carry less of it, thinner ones more; in practice a busy two-way market runs a low single-digit margin, while a thin or exotic one can carry several times that. The reason is confidence and liquidity: a market a book is sure of, with plenty of money on it, can be priced tight, whereas an uncertain or thinly-traded one is padded more heavily to cover the risk. That variation is why implied probabilities from two different markets cannot be compared until the margin has been removed from each. Removing it is called de-vigging, and the result is the fair probability the market actually expresses, stripped of the house's cut.
Overround, margin and hold: three different numbers
People use "overround" for two numbers. One is the total of a market's implied probabilities, also called the booksum. The other is the margin (what this page calls the vig): how far that total sits above 100%. Hold is the margin as a share of the total: in theory, the share of all money staked that the book keeps. Say which number you mean.
| Market | Implied probabilities | Overround (total) | Margin | Hold |
|---|---|---|---|---|
| American −110 on both sides | 52.38% + 52.38% | 104.76% | 4.76 points | 4.55% |
| Decimal 1.60 and 2.35 | 62.50% + 42.55% | 105.05% | 5.05 points | 4.81% |
In row one, each side is 110 ÷ (110 + 100) = 52.38%. Both sides together are 220 ÷ 210 = 104.76%, so the margin is 10 ÷ 210 = 4.76 points. If bettors stake 110 on each side, the book takes in 220, pays the winner 210 and keeps 10: a hold of 10 ÷ 220 = 4.55%.
On a tight market, margin and hold come out nearly equal, so they get swapped. On a wide market they split: a 20-point margin is a 120% total and a 20 ÷ 120 = 16.7% hold. Quoting the margin as the hold overstates it.
A total of exactly 100% has no margin. A total below 100% can happen, and its margin is negative: the prices together imply less than one certain outcome. For both, the vig calculator adds a note: nothing to remove.
For more, see why odds add up to more than 100%.
How we handle the vig
EsportsOdds publishes one de-vigged market line instead of raw prices. The outcomes of each market are rescaled to sum to 100%, so the margin is already taken out. How the line is built is documented in the methodology.
See the vig explained for the full method, worked through with a real example.
Measure it on any market with the free vig calculator, which shows the overround, the margin, the hold, and which outcome is carrying it.
Start free with a sandbox key: a fixed sample of past matches, no card.