Arbitrage Calculator
Enter two decimal prices and a total stake to see whether it’s an arbitrage, how to split the stake across both outcomes, and the guaranteed profit. Runs entirely in your browser.
What is arbitrage?
Arbitrage is when the combined prices on every outcome of a two-way market imply less than 100% probability. Different books disagree on the price, and occasionally their best prices together leave a gap. Stake each side in proportion and you get the same return whichever way it goes — a small locked-in profit rather than a gamble on the result.
The formula
stakeA = T × (1/A) ÷ inv
stakeB = T × (1/B) ÷ inv
return = T ÷ inv profit = return − T
where A and B are the two decimal prices and T is the total stake.
Worked example
Suppose outcome A is 2.10 and outcome B is 2.05, with a $100 total stake. Then inv = 1/2.10 + 1/2.05 ≈ 0.4762 + 0.4878 = 0.9640, which is below 1 — an arb. Stake ≈ $49.40 on A and ≈ $50.60 on B; either result returns about $103.74, a guaranteed profit near $3.74 (about +3.7%).
When to use it — and the catch
Use it when you’ve found the best price on each side of a two-way market across different books. In practice arbs are small and short-lived: prices move fast, one leg can change before you place the other, and books may limit accounts that arb heavily. Always confirm both live prices first, and treat the maths as the ceiling, not a promise.
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What is arbitrage betting?
Arbitrage — or an “arb” — is when the prices available on all outcomes of an event imply a total probability below 100%. By staking each outcome in the right proportion, you can lock in the same return no matter which result lands, for a small guaranteed profit.
How do you calculate a two-way arbitrage?
Add the inverse of each decimal price: inv = 1/A + 1/B. If inv is below 1 it’s an arb. Split a total stake T so stakeA = T × (1/A) ÷ inv and stakeB = T × (1/B) ÷ inv. The guaranteed return is T ÷ inv, and the profit is that minus T.
Is arbitrage betting legal in Australia?
Arbitrage itself is simply staking maths, not illegal. However, bookmakers may limit or close accounts they believe are arbing, and prices can move before you place both legs. This tool is for education and research, not betting advice.
Why did my arb disappear?
Arbs are usually short-lived. Odds move quickly, and one leg can shift before you place the other, turning a small guaranteed profit into a loss. Always re-check both live prices before staking.