Arbitrage

An arbitrage — an "arb" — exists when two sportsbooks disagree enough about the same event that you can back every outcome and profit whichever way it lands. It happens because books price independently and move at different speeds, so one can be slow to react to news the other has already priced in.

The test is simple. Convert each side's odds to implied probability and add them up. If the total is below 100%, the gap is the arb margin - the return if both bets are accepted and settled at those prices; at or above 100%, there is no arb and the excess is the books' combined margin. Two sides at +105 and -100 imply about 48.8% and 50.0%, totalling 98.8% — a 1.2% arbitrage. Stakes are split in proportion to each side's implied probability so both outcomes return the same amount.

The part most guides leave out: arbs are small, short-lived and operationally hostile. Returns are typically 1-3%, so meaningful profit needs large stakes across multiple funded accounts. Prices move while you are placing the second leg, and getting one side down without the other leaves you with an ordinary unhedged bet. Sportsbooks actively monitor for this and respond by limiting stake sizes or closing accounts, so the strategy tends to degrade the more successfully you run it. Voided legs, different rules on the same market between books, and settlement disputes can all turn an arb margin into a real loss.

None of that makes arbitrage a scam — the math balances both outcomes at the moment both bets are matched. It just means the practical constraints, not the arithmetic, decide whether it is worth doing. If your interest is finding mispriced numbers rather than hedging them, the best lines board compares every book on one screen, and the FAQ covers how a fair price is calculated once the vig is stripped out.