When two books disagree enough about the same event, backing both sides can guarantee a profit. The calculator tells you whether the gap is real and how to split the stake.
Odds format:
Add the implied probabilities of both outcomes across the two books you are using. If the total comes to less than 100%, the two prices together guarantee a profit regardless of the result. Split the stake in proportion to the implied probabilities and both outcomes return the same amount. The margin is small, typically a fraction of a percent to a few percent.
Sportsbooks price independently and move at different speeds. A line that shifts quickly at one book and slowly at another creates a temporary window. News, injuries and sharp money all cause these gaps. They close fast, which is the central practical difficulty rather than finding them in the first place.
Arbitrage reads as free money and behaves like work. Prices move while you are placing the second leg, leaving you with an unhedged position. Maximum stakes are often small on the side that is mispriced. Money has to sit idle across several books to be ready. And the margins are thin enough that a single mistake wipes out many successful arbs.
Sportsbooks identify arbitrage quickly and respond by limiting stakes or closing accounts. This is the reason most people who try it stop. A strategy that works for a few months and then leaves you unable to bet meaningful amounts anywhere has a cost that does not show up in the arithmetic.
Different books void or settle unusual situations differently, and two legs that should offset can end up not offsetting at all. Pay particular attention to rules on postponements, overtime, player withdrawals and void bets. An arb that becomes a single open position because one leg was voided is no longer an arb.
Typically a fraction of a percent to a few percent of the total stake. Larger gaps usually indicate an error somewhere, often a stale line about to be corrected or a rule difference you have not spotted.
Very likely. Books identify the pattern quickly and respond with stake limits or account closure. That consequence is the main reason arbitrage is harder to sustain than the maths suggests.
Getting one leg down and watching the price move before the second. You then hold an unhedged position you never intended. Rule differences between books on voids and postponements are the other common way an arb stops being an arb.
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