Arbitrage Calculator
When two books disagree enough, the best price on each side can cover both outcomes for less than you stand to collect — a sure bet. This arb calculator checks the condition across two books and, when a hedge exists, splits your stake so the payout is the same whichever way the game lands. Enter both books’ prices below; the sure-bet check runs live, every step shown.
Want live arb flags across your books as lines move? Open the Arb Finder tool in the app →
How the arbitrage calculation works
Start by converting the best price on each side to decimal odds — the total return per dollar staked, stake included. A bet at decimal odds d returns d dollars for every dollar risked, so its inverse is exactly the break-even probability the price implies:
Take the best available price on each side — side A from whichever book prices it highest, side B from the other — and add those two inverses. If the sum lands below one, the market is arbitrageable:
The shortfall below one is your locked margin: the fraction of total stake you keep no matter which side wins. To realize it, split the stake in proportion to each side’s inverse decimal odds, so both outcomes pay back the same amount:
Because the two stakes are sized so each side’s payout is identical, the return is the same whether side A or side B hits — that’s what makes it a hedge rather than a gamble on one outcome.
Worked example
Book A prices side A at +110 and Book B prices side B at +115. Take the best price on each side and convert to decimal:
The inverse sum is below one, so a sure bet exists. On a $1,000 total stake, split proportional to each inverse:
Why a “sure bet” rarely is
The arithmetic is clean; the execution is not. Arbs are a discontinuous threshold — one tick of line movement flips a locked gain into a locked loss — so they decay in seconds. A price can change between placing your first leg and your second, leaving you one-sided on a bet you never wanted alone. Stakes get voided, maximums get cut mid-click, and books routinely limit or ban accounts that arb. Treat the calculator’s margin as a best case that assumes both legs fill at the quoted prices, not a promise. The full method, execution risks, and the live scanner are covered in arbitrage betting.
Arbitrage is one of three edges built on the same de-vig foundation: it’s the discontinuous one. Compare it to the continuous +EV edge, size any single bet with the Kelly calculator, and strip the book’s margin from a single line with the no-vig calculator.
Frequently asked questions
What is an arbitrage calculator?
An arbitrage calculator checks whether the best available price on each side of a market, taken across two books, lets you cover both outcomes for less than you stand to collect. If the inverse decimal odds sum to less than one, a sure bet exists; the calculator returns the exact stake to place on each side so the payout is the same whichever way it lands.
How do you calculate an arbitrage bet?
Convert the best price on each side to decimal odds, then add their inverses. If that sum is below one, the market is arbitrageable. Stake each side in proportion to its inverse decimal odds — one over d divided by the total inverse sum — and both outcomes return the same amount. The gap between one and the inverse sum is your locked margin.
Is arbitrage betting risk-free?
The math is risk-free only if both bets land at the prices shown. In practice arbs decay in seconds as lines move, a price can change between placing the first and second leg and leave you one-sided, stakes can be voided, and books routinely limit or ban accounts that arb. Treat the locked margin as a best case, not a guarantee.