PuntersEdge Tools
Arbitrage Calculator Australia
Enter the best available price for each side of a two-way market and a total outlay. The calculator splits the stake so the return is identical whichever outcome wins, and shows whether a margin actually exists after you account for it.
Results will appear here.
How the calculation works
Convert each decimal price to its implied probability by taking the inverse, then add them together:
total implied probability = (1 ÷ oddsA) + (1 ÷ oddsB)
If that total is below 1.00, the two prices together imply less than a certain outcome, and an arbitrage exists.
Two figures get called “the margin”, and they are not the same number. 1 − total is the book's overround recovered. What you actually keep is (1 ÷ total) − 1 — the profit as a percentage of what you laid out. The calculator above reports the second, because that is the one that becomes money.
Each stake is then the outlay weighted by that side's share of the implied probability:
stakeA = outlay × (1 ÷ oddsA) ÷ total
Because the stakes are weighted this way, the return is the same whichever side wins — which is the entire point. If the total is above 1.00, the bookmakers' margin is intact and any split loses money on both outcomes.
Worked example
Outcome A at $2.10 and outcome B at $2.05 give implied probabilities of 0.4762 and 0.4878, totalling 0.9640 — below 1, so an arbitrage exists. On a $100 outlay you would stake $49.40 on A and $50.60 on B. Either result returns $103.73, a profit of $3.73, or 3.73% of outlay. (The overround recovered, 1 − 0.9640, is 3.60% — the smaller of the two figures, and the one that is not your return.)
Why the number on screen overstates it
A calculated margin is a ceiling, not a result. In practice it is reduced or erased by:
- Price movement between bets. You are placing two bets sequentially. If the second price shortens before you get on, the arbitrage can vanish or invert — leaving one-sided exposure rather than a locked position.
- Stake limits. The maximum a bookmaker accepts on the side you need is frequently smaller than the split requires, which caps the position rather than the percentage.
- Exchange commission. If one side is an exchange, commission applies to winnings on that side. Set it above to see the effect — a few percent commission removes most small margins.
- Account restrictions. Australian bookmakers may restrict or close accounts at their discretion, and commonly do so for patterns they identify as arbitraging. This is a term of service matter, not a legal one.
- Voided legs. If one side is voided and the other stands, the position is no longer hedged and becomes a straight bet.
A margin under about 2% is rarely worth acting on once these are priced in.
Frequently asked
Is arbitrage betting legal in Australia? Betting with licensed Australian bookmakers is legal and arbitrage is not itself an offence. Bookmaker terms, however, generally allow accounts to be limited or closed at the operator's discretion.
Why do opportunities disappear so fast? Prices move continuously. The practical difficulty is execution speed and stake limits, not spotting the price.
Does this work for three-way markets? This calculator handles two-way markets. The same method extends to three outcomes by summing three inverse prices.
Related: Odds Converter · Implied Probability Calculator · EV Calculator.
Working with live odds?
The hard part of this is not the arithmetic — it is having current prices from every book at once. PuntersEdge publishes live odds from 14 Australian racing bookmakers as a REST/JSON API, with next-to-go racing, runners and best-odds comparison, and every response carries its own age so you can see how fresh it is.
See API pricing · Developer docs · Get a free API key — 1,500 credits/month, no card.
18+ only. This calculator is for informational and educational purposes only and is not betting advice. No return is guaranteed. Gambling can be addictive. Gambling Help: 1800 858 858.