How do I know if two odds form an arbitrage?

Convert each price to implied probability (1 / decimal odds) and sum them. If the total is under 100%, backing every outcome at those prices guarantees profit. The margin is (1 / total) - 1.

How do I split my stake in an arbitrage bet?

Stake each outcome proportionally to its implied probability: stake_i = total stake x (implied_i / sum of implieds). Every outcome then returns the same amount.

How big are real sports betting arbs?

Real cross-book arbs are typically 0.5% to 3%. Anything larger usually means a stale line, a limit-restricted book, or a price about to be voided.

Arbitrage calculator

Is it an arb? Split the stake.

Last updated 2026-07-03

Enter the best available price on each outcome, from different books, in American odds. If the combined implied probability is under 100%, you have an arb; the tool splits your stake for identical profit whichever outcome wins.

Outcome 1 best price (e.g. DraftKings)

Outcome 2 best price (e.g. FanDuel)

Outcome 3 (optional, for 3-way markets)

Total stake

How it works

Sum of implied probabilities under 100% = guaranteed margin of (1 / total) - 1. Stakes are split proportionally to each outcome's implied probability so every outcome returns the same amount. Real cross-book arbs run 0.5-3%; a "10% arb" is almost always a stale line or a book that will void the bet.

Execution risks the math ignores: line moves between your two bets, stake limits, and account restrictions. Speed matters more than margin.

Do this programmatically

Finding arbs by hand means refreshing 50 sportsbook sites. One API call returns every book's price for every game, and the arbitrage endpoint precomputes the opportunities:

curl "https://api.theoddsapi.com/intelligence/arbitrage?sport_key=basketball_nba" \
  -H "x-api-key: YOUR_API_KEY"

Business tier. Full workflow in the arbitrage detection guide.

Questions

Why does my arb disappear before I place the second bet?

Arbs exist because one book is slow to reprice. The gap typically closes in seconds to minutes. Automated detection with a 30-second refresh feed is how serious arbers stay ahead of the close.

Do bookmakers ban arbitrage bettors?

Soft books limit or close accounts that consistently take one side of stale lines. Pinnacle welcomes winners. Factor account longevity into which arbs you take.

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