Free tool
Arbitrage Calculator
Two prices on opposite sides of the same market, at two different books. It splits your stake so the return is identical whichever way it lands — and tells you plainly when the numbers don't work, which is most of the time.
Enter both prices — opposite sides of the same market, at two different books.
Books limit and ban arbers. Arbing consistently gets accounts restricted or closed — a stake cap, then no market at all. An $11.75-style profit can cost you an account you wanted for years. Lines move. By the time the second bet is placed the first price may be gone, and a half-filled arb isn't an arb — it's just a bet, at a price you chose for arithmetic rather than because you liked it.
This site's scope is Michigan-legal books, so there are fewer books here than a global tool shows — and fewer arbs with them.
How it works
Each price implies a probability (1 / decimal odds). Add the two: if they come to less than 100% the books disagree by more than their own margin, and a split stake returns the same amount either way. At 100% or more there is no arb — the gap is the vig, and the "split" is a guaranteed loss.
Arbs are rarer and worth less than they look. Books limit and close accounts that do this consistently, and a line can move between your first bet and your second — leaving you with one leg at a price you only chose for the arithmetic.