An arbitrage (or "arb") exists when different bookmakers price the same event so that you can back every outcome and lock in a profit no matter what happens. This calculator takes the best available odds for each outcome, tells you instantly whether an arb exists, and splits your stake so every result returns the same amount.
How arbitrage betting works
Every set of odds implies a probability: 1 divided by the decimal odds. Add up the implied probabilities of every outcome across the best available books. If that total is below 100%, the market has mispriced the event and an arbitrage exists.
To capture it, you stake each outcome in inverse proportion to its odds, so that whichever result lands, your return is identical. The gap between that guaranteed return and your total stake is your locked-in profit.
The calculator handles this two ways: split a fixed total stake across all outcomes, or anchor one leg you have already placed and size the rest to match its return. Both produce an equal payout on every outcome.
Worked example
Suppose one book prices Team A at 2.05 and another prices Team B at 2.05. Implied probabilities: 1/2.05 + 1/2.05 = 0.4878 + 0.4878 = 0.9756, or 97.6%. Below 100%, so this is an arb.
Stake $100 total. The equal-return split puts $50 on each side. Whichever team wins, you collect $50 × 2.05 = $102.50.
Your profit is $102.50 − $100 = $2.50, a 2.5% return with no exposure to the result. Real arbs are usually this thin, which is why speed and stake sizing matter.