Every price at every Australian bookmaker has a hidden tax built into it called the vig. It's how bookmakers make money, and understanding it is the first step toward recognising which bets actually represent value and which just feel like they do.
This guide covers what the vig is, how to calculate it on any market, what normal vig amounts look like at AU bookmakers, and what the vig tells you about the quality of a given price.
What is vig, exactly?
Vig (short for vigorish) is the percentage by which the combined implied probabilities of all outcomes in a market exceed 100%. Other names for the same thing:
- Bookmaker margin — the most common term in Australia.
- Overround — technical term used in analytical contexts.
- Juice — American betting slang.
- Book percentage — specifically, the total implied probability; vig is book percentage minus 100.
All five terms describe the same thing: the built-in margin that makes the bookmaker mathematically favoured to profit over time regardless of customer outcomes.
The vig calculation formula
The formula is simple and works for any market:
Vig % = (Sum of implied probabilities of all outcomes) − 100%
Where implied probability of each outcome = 1 / decimal odds.
Two-way example: AFL H2H
Sportsbet has Collingwood at $1.91 and Essendon at $1.91 in an AFL H2H market.
- Collingwood implied probability: 1 / 1.91 = 52.36%
- Essendon implied probability: 1 / 1.91 = 52.36%
- Book percentage: 52.36% + 52.36% = 104.72%
- Vig = 104.72% − 100% = 4.72%
Three-way example: A-League soccer
A soccer match has three outcomes: home, draw, away. Example prices at Ladbrokes: Home $2.30, Draw $3.40, Away $3.20.
- Home implied probability: 1 / 2.30 = 43.48%
- Draw implied probability: 1 / 3.40 = 29.41%
- Away implied probability: 1 / 3.20 = 31.25%
- Book percentage: 43.48% + 29.41% + 31.25% = 104.14%
- Vig = 104.14% − 100% = 4.14%
Three-way vig at AU soccer markets is typically slightly lower than two-way vig because the competitive pressure between books on high-profile international soccer keeps margins tight.
What the vig tells you about a market
The vig percentage is a direct measure of how expensive a market is for you. Every percentage point of vig is a percentage point of expected loss per dollar staked, before any question of whether your pick is right.
Typical vig ranges at Australian bookmakers:
- AFL/NRL H2H mainline: 3-6% vig at most AU corporates.
- AFL/NRL line (spread) markets: 4-6% vig.
- AFL/NRL totals: 5-7% vig.
- NBA H2H: 4-6% vig.
- Soccer 3-way H2H (A-League, EPL): 3-6% vig.
- Player props (AFL disposals, NRL try scorer, NBA points): 8-15% vig.
- First try/goal scorer markets: 20-30% vig.
- Same-game multis (SGMs): 20-35% vig.
- Exotic markets (specific scorelines, anytime double): 15-25% vig.
The consistent pattern: main markets have low vig because competition between AU bookmakers drives margins down. Novelty and niche markets have much higher vig because retail punters don't price-shop on them.
Vig by AU bookmaker
Typical vig levels on mainline AFL H2H markets at AU bookmakers (observations from tracked pricing):
- Bet365: 3-4% — among the tightest in AU.
- Sportsbet: 4-5%.
- Ladbrokes / Neds: 4-5%.
- PointsBet: 4-6%.
- Unibet: 4-6%.
- TAB: 5-7% — consistently wider than the newer corporates.
- BlueBet / BetRight / Dabble: 5-8% on main, wider on props.
- Betfair Exchange: ~0% on the market (price is determined by users), replaced by 6.5% commission on net winnings.
Betfair's structure is fundamentally different. The exchange matches backers with layers at a market price, so there's no bookmaker margin baked into the odds. Betfair's economics come from commission on winning bets. For the full Betfair discussion, see the Betfair defence piece.
How to use vig to find value
Low-vig markets are structurally better to bet. If AFL H2H at Bet365 has 3.5% vig and the same market at TAB has 5.5% vig, the Bet365 price is closer to fair value — meaning your expected-value calculation against true probability is more favourable on Bet365 for the same market.
Specifically, two things matter:
Compare vig across bookmakers on the same market. Within AU, the price dispersion across 100+ bookmakers on the same AFL H2H can range from 3% to 7% vig on a single market. Always betting at the lowest-vig book for a given market compounds to meaningful EV differences across a season.
Compare your estimated true probability to the de-vigged price. Once you strip the vig out of a market, you get the fair odds — the bookmaker's estimate of true probability, stripped of margin. Your EV calculation should compare your true probability estimate to the fair (de-vigged) probability. See the de-vigging guidefor the mechanics.
Vig traps to avoid
A few ways bettors accidentally expose themselves to high-vig products:
Same-game multis. SGMs compound vig across legs and add correlation-based margin. Typical AU SGMs run 25-35% effective vig. Even +20% promotional boosts rarely make them mathematically profitable. See the multis piece.
First goal scorer / first try scorer markets. Novelty markets with 20-30% vig. Occasionally beatable through specific mispricings but hostile terrain generally.
Specials and exotic markets. “Will there be a player sent off,” “total corners over/under,” “correct score.” Narrow audiences, wide vig.
In-play phone betting. Phone bets at AU corporates carry wider margins than pre-match online prices — a structural consequence of the operational cost of phone betting plus the reduced competitive pressure.
Related calculations
Vig calculation is the foundation under several related techniques:
De-vigging: removing the vig from a set of odds to produce fair (no-vig) probabilities. See the de-vigging guide.
Arbitrage detection: finding combinations of best-available prices across bookmakers where the combined book percentage falls below 100%. See the surebet beginner's guide.
Expected value calculation: comparing your true-probability estimate to the bookmaker's implied probability to determine if a bet is +EV. See the EV calculation guide.
Frequently asked questions
Is lower vig always better?
Yes, mathematically. Lower vig means prices closer to fair value, which means your EV calculations are more favourable. For the same true probability estimate, a lower-vig price always produces higher EV.
How do I calculate vig on three-way markets?
Same formula as two-way: sum the implied probabilities of all three outcomes (1 / odds for each), subtract 100%. For a soccer market at $2.40, $3.40, $3.20 the book percentage is 43.48% + 29.41% + 31.25% = 104.14%, vig is 4.14%.
What's the difference between vig and overround?
They're the same concept. “Vig” is US/AU betting slang, “overround” is the technical term used in bookmaking and analytics. Book percentage minus 100 equals both.
Does Betfair have vig?
Betfair Exchange doesn't have traditional vig because prices are set by users matching against each other. Betfair's economics come from a 6.5% commission on net winnings, which has a similar effect on bettor returns as vig does at conventional bookmakers. On net, Betfair is usually slightly better value than AU corporates on main markets despite the commission.
Can you find zero-vig markets?
Not at conventional bookmakers in normal conditions. Zero or negative combined book percentage across multiple bookmakers is an arbitrage opportunity and disappears quickly. See the arbitrage guidefor the mechanics.
James covers the AU bookmaker market — pricing mechanics, line movement, promotional structures, and how the corporate books actually operate. Previously worked in financial markets before moving to sports analytics.