Arbitrage Betting

Arbitrage betting, or "arbing," is placing bets on every outcome of an event at different books, at prices good enough that you profit no matter the result. It is not a prediction. It is a pricing inefficiency you exploit with arithmetic.

When an arb exists

Convert each price to its implied probability, 1 / decimalOdds, and add them up. If the total is below 100%, an arb exists. The amount below 100% is your margin. Formally, for two opposing prices the arb margin is 1 - (1/decimalA + 1/decimalB). A positive margin is risk-free profit; a negative margin is the hold you would pay to bet both sides at a single book.

Arbs appear because books disagree. One book moves a line on sharp action while another lags, and for a short window the two best prices overlap into a guaranteed profit. Prediction-market exchanges, which price independently of sportsbooks, widen the field of disagreement, which is why they create more of these windows.

Sizing the stakes

To lock equal profit either way, split your total stake in proportion to each side's implied probability. Our Arbitrage Calculator does the split and shows the guaranteed profit; the live hedge finder scans every book we track and surfaces the arbs for you, so you do not have to hunt.

The practical risks

The math is risk-free, the execution is not. Three things bite arbers:

• Lines move. A price can change between placing your two bets, breaking the arb. Place the more volatile side first and move quickly.
• Limits and bans. Books profile and limit accounts that consistently arb. This is the real ceiling on arbitrage as a strategy.
• Exchange depth. On a thin prediction market, a large stake can slip to a worse price than the screen showed. Confirm depth before sizing up.

A worked example

Suppose Book 1 prices Outcome A at +120, which is 2.20 in decimal, and Book 2 prices the opposite Outcome B at +110, or 2.10. The implied probabilities are 1/2.20 = 45.5% and 1/2.10 = 47.6%, summing to 93.1%. That is below 100%, so the arb margin is about 6.9%. On a 100 stake, you put roughly 48.85 on A and 51.15 on B; either result returns about 107, locking close to 7 in guaranteed profit no matter who wins. Change Book 2 to -110 instead and the two implied probabilities sum to over 100%, the margin goes negative, and betting both sides would simply hand the books their hold.

Arbitrage is closely related to expected value: an arb is simply a collection of bets whose combined EV is guaranteed positive. The cleaner mental model for most bettors is to chase +EV bets one at a time and treat arbs as the rare moments when the edge is locked. Either way, the prerequisite is the same: see every book's price at once, which is what a live line-comparison board gives you.