How bookmakers work and make their money

A bookmaker works by setting a fixed price on every outcome, taking bets against those prices and building a margin into them, so the chances its odds imply add up to more than 100%. Over enough bets it pays out less than it takes in, whichever way any one race or game goes.

A bookmaker also has to manage what it stands to lose on each result, decide whose bets it wants, fund its promotions, and pay tax and racing's fees out of what the margin brings in. Each of those shapes the prices and limits you see in your account.

How the margin is built into the prices

Every decimal price implies a chance: implied probability = 1 / decimal odds. In a market with no margin, the implied chances of all the outcomes add to exactly 100%. A bookmaker shortens each price a little, so the total runs over 100%, and the excess is the overround, which most punters call the margin.

With illustrative prices for a tennis match, where only two outcomes are possible:

The overround is 104.17% - 100% = 4.17%. The share of turnover a book balanced at those prices keeps is a smaller number, because it is measured against everything staked: 1 - 1 / 1.041667 = 0.04, or 4.0%. A race with a dozen runners spreads its margin across every price, rarely evenly. Bookmaker margin works through bigger markets, and the bookmaker margin calculator reads the margin out of any set of prices.

Balanced books, lopsided books and liability

A balanced book has stakes on each outcome in proportion to its implied chance, so the bookmaker pays out the same amount whichever outcome wins. A lopsided book has too much money on one side, so one result costs it money. That potential loss, counted across every bet in the market, is the bookmaker's exposure on the result, which bookmakers also call their liability. Here is $12,500 of illustrative turnover on the same match, arriving two ways:

The balanced book makes $500 either way. The lopsided one carries a $1,900 liability on Player A, yet it still expects about $500 on average, provided its prices are right. Take the margin out proportionally, scaling each chance down by the same factor, and Player A's fair chance is 0.625 / 1.041667 = 0.60. The expected result is then 0.60 x -$1,900 + 0.40 x $4,100 = -$1,140 + $1,640 = $500. Other de-vig methods give a slightly different fair chance, and so a slightly different expected result.

Suppose instead that Player A's real chance is 66%. The same book now expects 0.66 x -$1,900 + 0.34 x $4,100 = -$1,254 + $1,394 = $140. Each dollar bet on Player A at $1.60 now costs it 0.66 x 1.60 - 1 = 0.056, or 5.6 cents, on average. A bookmaker's long-run profit depends on prices close to the real chances, and on not taking too much money from the customers who can tell when they are not.

Setting prices or following them

Bookmakers get their prices in two broad ways, and most mix them.

A market maker frames its own prices. Odds compilers or models set the opening market, traders adjust it as money arrives, and the business carries the risk of being wrong. Because it prices first, a market maker also learns from the bets it takes: sharp money moving its price is information, bought at a cost.

A follower takes its prices from elsewhere, such as other bookmakers or a betting exchange, and competes on margin, promotions, limits or service instead. Many smaller brands run on shared betting platforms, which is one way two brands can show identical prices. A shared licence holder or owner is a separate matter that says nothing about prices on its own: who owns Australian bookmakers sets out each brand's licence holder from ACMA's register and its parent group as reported.

How bookmakers set odds covers the pricing methods, and sharp vs soft bookmakers covers why the two kinds treat winning customers so differently.

How risk teams manage liability and limits

A bookmaker's risk or trading team watches the liability on every outcome. When one result gets too expensive, it has four main levers:

1. Move the price. Shortening Player A from $1.60 to $1.50 cuts what each new bet on A costs if A wins, and lengthening Player B draws money to the other side.
2. Cap the stake. Each market has a maximum bet, and each account can be given its own share of it, a practice called stake factoring.
3. Refer the bet. A large bet can go to a trader, who accepts it, takes part of it or refuses it.
4. Lay it off. The bookmaker bets the same outcome somewhere else, so a loss on its own book is partly covered by a win on that bet. In NSW, an on-course bookmaker fielding at a racecourse can apply to Racing NSW, and to Liquor & Gaming NSW for a betting back approval, to place these bets online with licensed wagering operators.

Limits are also set customer by customer. The lopsided book above is only a real problem when the money on one side came from people who were right, so accounts whose bets keep beating the prices tend to get smaller limits. Why bookmakers restrict accounts covers how that works and what rights you keep, including the minimum bet limits set for racing bets.

What promotions cost and the rules they follow

Promotions are a marketing cost, paid out of the margin, and in Australia they work mostly on existing customers. Since 26 May 2019 (26 November 2019 in NSW), the National Consumer Protection Framework has barred bookmakers from offering anything of value, credit, vouchers and rewards included, as an incentive to open an account or to bring someone else in. What is left are offers to existing customers, such as bonus bets, money back offers, bet boosts and multi promotions, each under the bookmaker's own terms.

A bonus bet costs the bookmaker less than its face value, because a stake-not-returned bonus bet pays only the winnings, and only when it wins.

The framework also sets rules the cost has to fit inside. A bonus bet's winnings have to be withdrawable with no turnover requirement attached, and direct marketing may go only to customers who gave express consent, with an unsubscribe that works. Those rules sit beside the protections every online bookmaker owes you, such as deposit limits and monthly activity statements.

From 1 January 2027 the Interactive Gambling Amendment (Gambling Reform) Act 2026 stops providers paying staff or affiliates commissions tied to customer activity. It also bans direct-marketing inducements to new account holders, people identified as at risk of gambling harm and people who have left BetStop. That ban applies only from a later day the Minister sets by notifiable instrument (checked October 2026). Bonus bets explained covers how the bets themselves work.

Taxes and fees paid out of the margin

Wages, technology and advertising come out of the margin like any business's costs. Three costs are particular to wagering:

Point of consumption tax is the operator's tax, not the punter's: it is not taken out of your winnings, and each state revenue office publishes its own rate. Race field fees fund racing and come with conditions. An operator that uses NSW thoroughbred race fields must have Racing NSW's approval wherever it is licensed. The racing bodies that set minimum bet limits attach them to approvals like that one, and in Western Australia licence conditions do the job. Those conditions are why racing bets carry rules that sports bets do not.

How totes and exchanges make money instead

Not every betting business takes the other side of your bet:

A tote's commission comes off the pool before anyone knows the dividend, which is declared after the result, so the operator needs no view on the race. An exchange charges commission at a rate it sets on each customer's net winnings in a market. The TABs run tote pools and sell fixed odds too, so one company can earn both ways. Betting exchanges in Australia and fixed odds vs tote cover each in more depth.

Comparing prices across bookmakers

Because each bookmaker builds or copies its prices with its own margin, the same runner or team can sit at different prices at the same moment. Taking the higher price on the same bet gives up less of the margin.

On the Terminal, prices from 40+ bookmakers across racing and sports sit next to each other and next to Betfair back and lay, with the best available price on each runner picked out. Because the board is refreshed on a repeating cycle, a price on it can lag the bookmaker's own, so check with the bookmaker before you place anything. A free account opens a limited view of the Terminal with live odds. Bookmaker names are trade marks of their owners. B337 is not affiliated with them.