Arbitrage Calculator: Find and Size a Surebet

Arbitrage betting means backing every outcome of an event at different sportsbooks so that you profit whatever happens. It works when books disagree enough on the price. This arbitrage calculator tells you whether a surebet exists, how to split your stake and what you will make.

The arbitrage formula

1. Convert each outcome’s best available price to decimal odds.
2. Add up the implied probabilities: A = 1/odds₁ + 1/odds₂ (+ 1/odds₃ for three-way markets).
3. If A is below 1, you have an arbitrage.
4. Profit margin = (1 ÷ A) − 1.
5. Stake on each outcome = total stake × (1/odds) ÷ A.

Worked example: an NBA moneyline arb

Sportsbook A has Team X at +110. Sportsbook B has Team Y at +105.

• Team X: +110 = 2.10 decimal, implied 47.62%
• Team Y: +105 = 2.05 decimal, implied 48.78%
• Total A = 96.40%, below 100%, so an arb exists
• Profit margin = 1 ÷ 0.9640 − 1 = 3.74%

With $1,000 to deploy:

Either way you finish about $37 ahead. In practice you would round stakes to whole dollars to look less like an arbitrage bettor, accepting a few cents of difference between outcomes.

The risks no calculator shows

• Prices move. Arbs often last seconds. If one bet is accepted and the other line moves before you place it, you are holding a one-sided bet.
• Palpable errors. If an arb comes from an obvious mistake, the book may void that bet under its house rules, leaving you exposed on the other side.
• Account limits. US sportsbooks restrict accounts that consistently take stale prices. Arbitrage has a shelf life.
• Different rules. Overtime, retirements in tennis and void conditions can differ between books, turning a sure thing into a loss.
• Capital. Your money is split across several accounts in your state. Our US betting guides list which books operate where.

When to use an arbitrage calculator

• To verify an arb flagged by software such as OddsJam or OddsShopper before you commit. Our AI betting tools guide compares them.
• To check a gap between a prediction market and a sportsbook. Remember to subtract exchange fees. See our Polymarket review for how its fees work.
• To split a stake across a three-way soccer market, where the draw adds a third leg.
• To see why a generous-looking market is not. If the total is above 100%, there is no arb, only two prices. Our implied probability calculator shows the margin.

How arbitrage software fits in

Finding arbs by hand means checking dozens of books every few minutes. Paid scanners do it continuously and flag gaps as they open. OddsJam, for example, cites an average return of 2 to 3% per pre-match arb and recommends a bankroll of $2,000 or more. The calculator above is your final check before you commit money. A scanner’s numbers can lag a moving line by a few seconds.

Always place the side most likely to move first, usually the price at the softer book, then confirm the other leg at once.

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