Bookmaker Margins Explained: How Bookies Always Win

Ever wondered how bookmakers always seem to win, even when punters occasionally beat them on individual bets?

The secret isn't luck. It's mathematics.

Australian bookmakers like Sportsbet, TAB, Ladbrokes, and Bet365 use a built in profit mechanism called the bookmaker margin, aka vigorish (vig) or juice. This mathematical edge guarantees they profit regardless of which team wins or what outcome occurs.

Understanding how bookmaker margins work is essential for anyone serious about sports betting in Australia. It's the foundation for identifying value bets, calculating expected value, and ultimately beating the bookies at their own game.

How Do Bookies Set Odds?

Bookmakers use teams of analysts and statistical models to determine the probability of different outcomes occurring. These probabilities are then converted into the odds you see offered to customers in decimal, fractional, or American format.

How Do Odds Change?

Odds move for one main reason: when lots of money comes in on one outcome, bookmakers adjust the odds to encourage betting on the other side. This allows them to maintain their set profit margin on both outcomes.

How Do the Bookies Win? (Bookmaker Margin)

The bookmaker margin is the bookmaker's built in profit margin for each bet offered.

For example, in an AFL head to head match, if they determine both teams have a 50% probability of winning, the fair odds should be $2.00 for each team. However, they might only offer $1.90 for both teams instead.

To calculate the margin for a market with two outcomes:

(1/1.90) + (1/1.90) = 1.053, which equals 105.3%

The extra 5.3% above 100% is the bookmaker's margin. This means for every $100 wagered across both outcomes, the bookmaker earns $5.30 in profit regardless of which team wins.

The margin is typically 3-5% on popular leagues and markets like head-to-head in AFL, NRL, and cricket, but can be 10% or higher on less popular leagues and markets such as player props.