When a bookmaker moves Collingwood from $1.90 to $1.80, most punters barely notice. The price changed. It still looks like a reasonable bet. The difference — 10 cents per dollar — feels trivial. It is not. That 10c shift doubles the vig on your bet and doubles your expected loss rate over time. The pricing decisions bookmakers make every day — which side to shade, when to move a line, how much margin to embed in a multi — compound across your bets into real money. Understanding how those decisions work is the first step to minimising their impact on your bottom line.
The vig: where your money goes
Every bet at a corporate bookmaker includes a margin — the vig. On a standard two-outcome market priced at $1.91 each side, the vig is approximately 4.7% of the total market. Per side, it is roughly 2.35%. This means that on a 50-50 proposition, you lose about 2.35 cents per dollar staked per bet, on average. At even win-loss rates, you lose 4.5 cents per dollar.
That is the standard rate. But the vig is not constant across all markets and all prices. Here is the actual vig per bet at different price points for a two-outcome market where both sides are priced equally:
- $1.95 each side: vig ≈ 2.6% per market (1.3% per side) — tight, good price
- $1.91 each side: vig ≈ 4.7% per market (2.35% per side) — standard AU price
- $1.87 each side: vig ≈ 7.0% per market (3.5% per side) — expensive
- $1.80 each side: vig ≈ 11.1% per market (5.6% per side) — very expensive
- $1.70 each side: vig ≈ 17.6% per market (8.8% per side) — punitive
The jump from $1.95 to $1.87 — an apparently small 8-cent difference — nearly triples the vig. The jump from $1.91 to $1.80 more than doubles it. The price you accept has a larger effect on your long-term result than your win rate does, within any realistic range of win rates.
See the full vig explainer for the calculation mechanics across different market types.
The favourite-longshot bias: why the same market has different margins
Not all bets in the same market carry the same vig. Bookmakers deliberately apply different margins to different price points within the same market. This is the favourite-longshot bias.
In an AFL head-to-head market with a strong favourite:
- Collingwood (favourite): $1.50 — implied probability 66.7%
- Essendon (underdog): $2.60 — implied probability 38.5%
- Book percentage: 66.7% + 38.5% = 105.2% → 5.2% vig
But the vig is not distributed evenly. If the true probability is Collingwood 64% and Essendon 36% (fair prices $1.56 and $2.78), the bookmaker has loaded more vig onto the favourite:
- Collingwood: fair $1.56 vs offered $1.50 → 3.8% vig on this side
- Essendon: fair $2.78 vs offered $2.60 → 6.5% vig on this side
Wait — the longshot side has more vig in this example? The direction of the bias varies by sport and market. In Australian sports (AFL, NRL), the favourite-longshot bias often favours the longshot — the underdog price is closer to fair value because the bookmaker needs to attract money to that side. In US sports (NBA, NFL), the bias often favours the favourite because American recreational punters bet favourites more heavily. The direction is not universal. The existence of the bias — that margins are not applied symmetrically — is universal.
The practical implication: you cannot assume that the vig is the same on both sides of a market. If you are betting favourites in AFL, you might be paying less vig than expected. If you are betting underdogs in NRL, you might be getting a better deal than the headline odds suggest. The only way to know is to de-vig the market and compare each side to your own probability estimate. See the devigging guide for the method.
Line movement: when the bookmaker adjusts and what it costs you
Bookmakers move lines for three reasons:
Information-based movement. New information arrives (team news, injury update, weather change) and the bookmaker adjusts the price to reflect the changed probability. This movement is legitimate — the new price is a more accurate reflection of the true probability given the new information. If you bet before the movement at the old price, you got a better deal. If you bet after, you are getting the market price. There is no systematic edge on either side.
Volume-based movement. The bookmaker has taken disproportionate volume on one side and moves the line to attract balancing money. This movement is not driven by new information about the outcome — it is driven by the bookmaker's position management. If you are betting the side that has attracted heavy volume, you are betting into a line that is about to move against you. If you can identify which side is attracting heavy recreational volume (favourites, popular teams, prime-time games), you can bet the other side before the move — or wait for the move and bet the popular side at a better price.
Competitor-following movement. The market leader moves and the followers adjust. No new information. No volume imbalance. Just a mechanical adjustment to stay within the market spread. This movement creates the middle windows that middle bettors exploit — the slow follower still has the old price. See the middle betting guide.
Multi-leg pricing: where the margin really lives
Multi-leg bets (multis, parlays, accumulators) are the bookmaker's highest-margin product. The vig compounds across each leg:
- 2-leg multi of $1.91 legs: combined vig ≈ 9.3%
- 3-leg multi: combined vig ≈ 13.6%
- 4-leg multi: combined vig ≈ 17.7%
- 5-leg multi: combined vig ≈ 21.5%
These are the standard multi numbers where each leg is independently priced. Same-game multis are worse. The bookmaker applies an additional correlation discount — a reduction in the multi price to account for the fact that the legs are correlated (if one leg wins, the probability of the other legs winning changes). The correlation discount is deliberately conservative, meaning the bookmaker builds in extra margin to protect against model uncertainty on the correlation. The combined margin on a same-game multi can exceed 30%.
The bookmaker promotes multis heavily — boosted odds, multi specials, "same game multi" as a featured product — precisely because they are the most profitable product. The marketing push is inversely correlated with the value to the punter. The more a bookmaker promotes a bet type, the more margin is embedded in it. See the multi analysis for the full breakdown.
Promotional pricing: when the bookmaker deliberately offers value
Sometimes a bookmaker offers a price that is above fair value — an odds boost, an enhanced price, a money-back special. These promotions are not pricing errors. They are marketing expenses. The bookmaker is deliberately offering a +EV bet to attract customers, knowing that the lifetime value of an acquired customer (who will go on to bet at standard minus-EV prices) exceeds the cost of the promotional offer.
The strategy for the punter: take the promotional +EV offers and nothing else. Place the boosted bet. Do not place additional bets at standard prices alongside it. The bookmaker's model depends on the promotional bet being the entry point to a longer relationship where the punter bets at standard margins. If you only take the +EV offers and never bet at standard prices, you are exploiting the bookmaker's customer acquisition cost. See the promo arb guide for the full strategy.
Frequently asked questions
Why do odds keep shortening after I place my bet?
This is not a conspiracy. Two things are happening. First, confirmation bias: you remember the times the odds shortened after you bet (feels like validation) and forget the times they lengthened (feels irrelevant or you did not check). Second, if you are betting popular sides (favourites, well-known teams, prime-time games), the volume of recreational money on those sides pushes the line down. The bookmaker shortens the price not because the probability changed but because the volume is coming in on that side and they need to manage their exposure. Your bet was part of the volume that caused the move. This is why betting early in the week (before the recreational volume arrives on Friday-Saturday) often gets better prices on popular sides — and betting against popular sides later in the week often gets better prices.
How much difference does price shopping actually make?
The difference between accepting the first price you see and checking three bookmakers is approximately 3-5% of turnover for the average punter betting major Australian sports. At $10,000 annual turnover (100 bets at $100 each), that is $300-$500 per year. At $50,000 annual turnover, $1,500-$2,500. The price-shopping habit requires having funded accounts at 4-6 bookmakers and the discipline to check before every bet. It is the single highest-ROI activity in sports betting — the edge is purely operational, requires no analytical skill, and compounds across every bet you place. See the odds comparison piece for the method.
Tom has been punting in Australia long enough to have strong opinions about most of it. Writes the opinion column — multis, Betfair, why your mate is wrong about betting, and the cultural side of being a sharp AU punter.