The betting margin, sometimes called the vigorish or juice, is the mechanism by which a bookmaker prices a market to favour itself. Rather than offering odds that reflect the true probabilities of outcomes, the operator shortens the prices slightly so that the implied probabilities across all outcomes add up to more than 100%.
The surplus above 100% is the margin. It can be expressed as a percentage and represents the operator’s theoretical hold on the market, assuming balanced action across outcomes. For the bettor, it is effectively a transaction cost embedded in every price.
Consider a hypothetical two-way market, such as a tennis match with two players. A fair, margin-free market might price each player at decimal odds of 2.00, where each implies a 50% probability and the two sum to exactly 100%. To introduce a margin, the bookmaker might instead offer both at 1.90. Each 1.90 price implies 1 ÷ 1.90 = 52.6%, and the two together sum to roughly 105.3%. The margin here is approximately 5.3%.
A common misconception is that a lower headline margin always means better value on a specific bet. Margins are not always applied evenly: operators may load more margin onto favourites, underdogs or particular selections, so the effective cost of an individual wager can differ from the market-wide figure. Examining the specific price matters as much as the overall margin.
Margins vary considerably between operators, sports, bet types and jurisdictions. High-volume markets such as major football matches tend to carry tighter margins, while niche or exotic markets often carry wider ones. Over many bets, the margin is one of the largest and most predictable drags on a bettor’s returns, which is why comparing prices across operators is a core habit of value-focused bettors.