Every bookmaker price contains a hidden tax — the overround, or bookmaker margin. It's the difference between the "fair" probability of an outcome and the probability the price implies. A market with no margin would have implied probabilities summing to exactly 100%. A real Australian H2H market typically sums to 104–108%. That extra 4–8% is the house edge, deducted from your edge before the ball is even bounced.
The maths in one line
If a bookmaker's two-way market has a 7% overround, the average price across the market is roughly 7% worse than fair. A model edge of 5 pp at fair prices becomes a −2 pp loss at that bookmaker. The pick was correct. The price killed it.
Worked example — same pick, four books
Same AFL H2H market, same selection. True probability (the model's posterior): 54.0%. Here are the prices on offer the morning of the game:
The edge at Book A is +3.0 pp. At Book D, it's +6.4 pp. The "tipster pick" is identical. The bet at Book A returns roughly half the long-run expected value of the bet at Book D.
Why tipster picks look better than they are
Tipster track records are almost always quoted at best-available odds at time of publication — odds you may not be able to access yourself. By the time the pick reaches you, the market has often moved. The published 5 pp edge becomes 1–2 pp at your book. Over 500 picks that gap is the difference between +15% ROI and −2% ROI.
Margins by market
H2H markets on the major footy codes are the most efficient — and the most likely place a real edge actually survives the margin. Same-game multis are the worst: a 25% margin on a four-leg multi means you'd need a 25 pp edge across the bet just to break even.
What to do instead
1. Hold accounts at 4+ bookmakers
The price gap between the best and worst book on any given market is typically 4–8%. You need to be on the right side of that gap.
2. Use the Bookmaker Grid
On every market the Edgewise terminal shows live prices across the major AU books, and highlights the best one. Click the best price to log it directly to your ledger at the price you actually took.
3. Track CLV, not ROI
If your average taken price beats the closing line by > 0%, you have edge — regardless of any individual result. CLV stabilises in ~50 bets; ROI takes 500+.
4. Stop betting same-game multis
The combined margin on a 4-leg multi is the bookmaker's most profitable product. There is essentially no model in the world that beats a 25% margin consistently. They exist to entertain, not to invest.