Arbitrage betting in Australia, explained
Arbitrage is bookie v bookie: no exchange needed. An arb is when bookies disagree on a price by enough that you can back every outcome and lock in a small return whatever happens. They're rare, small and short-lived, and bookies don't love them, but the maths is simple.
Step 1: turn odds into implied probability
Implied probability = 1 ÷ decimal odds. $2.00 is 50%, $1.80 is 55.6%, and $2.10 is 47.6%.
Add up the implied probabilities of every outcome in a market. With one bookie, it'll be over 100%; that's their margin. If the best prices across different bookies add up to under 100%, you've got an arb.
Step 2: worked example
A two-way tennis match: Player A is $2.10 at Bookie 1, and Player B is $2.05 at Bookie 2.
1 ÷ 2.10 = 0.4762, and 1 ÷ 2.05 = 0.4878. The total is 0.964, under 1, so it's an arb worth about 3.7%.
To split $100: stake A = $100 × 0.4762 ÷ 0.964 = $49.40, and stake B = $50.60. If A wins, $49.40 × 2.10 = $103.74. If B wins, $50.60 × 2.05 = $103.73. That's about $3.70 profit either way, before any rounding.
General stake-split formula (2-way or 3-way): stake on each outcome = total stake × (1 ÷ its odds) ÷ (sum of 1 ÷ odds across all outcomes).
3-way example (home/draw/away): $2.60, $3.60 and $3.40 at three different bookies. The sum is 0.3846 + 0.2778 + 0.2941 = 0.9565. On $100, that's $40.21, $29.04 and $30.75, each returning about $104.55.
Real arbs are usually smaller than this, often 1–2%.
The risks nobody puts on the brochure
- Odds move. If you get one side on and the other price drops before you place it, you're exposed.
- Obvious-error rules ("palps"). If a price was a mistake, a bookie may void or re-settle that leg.
- Different settlement rules, like retirements in tennis or overtime in the NFL and NBA, can leave one leg voided and the other live.
- Account limits. Arbing is the fastest way to get limited by Aussie bookies.
- Bet caps mean you might not get the full stake on.
Middles
A middle is a cousin of the arb: two different lines on the same game (say, a total of 210.5 at one bookie and 214.5 at another) where you can win both bets if the result lands in between. It's not risk-free, but it can be good value. Our Matched Betting & Arbitrage channel covers arbs and middles.
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