An arb is two books disagreeing in your favor.
Every sportsbook prices a market so that the two sides add up to more than 100 percent. Now and then, the best price on one side at one book and the best price on the other side at a different book add up to less than 100 percent between them, and covering both becomes a locked return. This page explains the math, the stake split, and the reasons it is harder to run than it sounds.
What arbitrage betting is
Arbitrage betting, often shortened to arbing, means backing every outcome of a market at prices that between them imply less than 100 percent probability. Because the outcomes are exhaustive, one of them has to happen, and if the stakes are sized correctly the same amount comes back regardless of which one does.
The test is a single addition. Convert both prices to implied probability and add them. Inside one sportsbook that sum is always above 100 percent, because the book's juice is built into both sides. Across two books that disagree, it can occasionally dip below.
The math on a real-sized arb
Suppose one book posts a side at +115 and a different book posts the opposing side at -105. The first implies 100 divided by 215, or 46.51 percent. The second implies 105 divided by 205, or 51.22 percent. They sum to 97.73 percent, which is below 100, so an arbitrage exists and the margin is the missing 2.27 points.
Sizing follows from those same numbers. Each side takes its own implied probability divided by the total, so on 1,000 dollars the +115 side gets 46.51 divided by 97.73, which is 475.90 dollars, and the -105 side gets the remaining 524.10 dollars. If the +115 side wins, 475.90 at those odds returns 1,023.19. If the -105 side wins, 524.10 returns the same 1,023.19. Either way the profit is about 23 dollars on 1,000 staked, which is 2.3 percent.
Notice how modest that is, and notice that splitting the 1,000 evenly instead would have produced a profit on one outcome and roughly break-even on the other. The proportional split is not a refinement, it is the whole mechanism.
Why locked profit is harder than it looks
Execution risk is the main one. An arb requires two bets placed at two books at almost the same moment. Get one down and lose the other to a price change or a rejected slip, and you are simply holding a normal wager on one side, sized as if you were hedged when you are not.
Capital sits idle. Running arbs of two percent at any meaningful scale means funding several accounts and leaving money in all of them, and that money is unavailable for anything else while it waits.
Books notice. Taking the top price within seconds of it appearing, in unusual stake sizes, across markets you otherwise never touch, is a recognizable pattern. The typical response is reduced limits or a restricted account rather than anything dramatic, but a limited account cannot run the strategy that got it limited.
Rules differ between books. Two sportsbooks can settle a suspended game, a withdrawn player, or a shortened baseball game differently, and when they do the two halves of a supposedly hedged position stop cancelling out.
Arbitrage and positive EV are different strategies
The two get mentioned together because both start with price shopping, but they behave nothing alike. An arb takes both sides and returns a small, certain amount. A positive EV wager takes one side at a price better than fair value, loses often, and relies on the average being favorable across a long run of similar decisions.
Practically speaking, arbs are rarer, smaller, and more operationally demanding, while +EV opportunities are more plentiful and require the patience to sit through losing stretches. Both depend on the same underlying habit, which is knowing what fair value is before you look at what is being offered.
MySpariEdge does not run an arbitrage service and does not place wagers. What our odds board does is show the same market at every book we track on one screen, which is the raw material any price-based approach starts from.
Arbitrage betting, answered
What is arbitrage betting?
Arbitrage betting means backing every outcome of the same market at different sportsbooks, at prices good enough that the combined implied probability comes to less than 100 percent. When that condition holds, the payouts can be arranged so the same amount is returned whichever result lands, and the difference is a locked profit.
How do you know if an arbitrage exists?
Convert each side's price to implied probability and add them together. If the total is below 100 percent, an arb exists and the shortfall is the margin. If the total is above 100 percent, which is the normal state of any single book's market, there is no arb because the sportsbook's vig is in the way.
How are the stakes split in an arb?
Each side is staked in proportion to its implied probability divided by the sum of both. That is what equalizes the return across outcomes. Splitting the money evenly instead leaves you with a profit on one result and possibly a loss on the other, which is not an arbitrage at all.
How big are arbitrage margins in practice?
Small. Most genuine arbs on liquid markets sit somewhere between half a percent and three percent of the total staked, and they usually appear because two books disagree briefly rather than because either one is badly wrong. Anything advertised as a very large arb usually turns out to be a stale price or a mismatched market.
Is arbitrage betting legal?
Placing bets at licensed sportsbooks in a jurisdiction where betting is legal is legal, and taking two sides at two different books does not change that. It can, however, breach a sportsbook's own terms of service, which is a contractual matter between you and that book rather than a legal one.
Why do sportsbooks limit arbitrage bettors?
Because the pattern is easy to detect and unprofitable for them to serve. Repeatedly taking the best available price moments after it appears, in odd stake sizes, on markets you have never touched before, looks distinctive in a risk report. Books respond by cutting limits or restricting the account rather than by voiding wagers.
What can go wrong with an arb?
The usual failure is execution. One leg gets placed and the second price moves or the bet is rejected before you can complete the pair, which leaves you holding an ordinary one-sided wager. Other risks include one book voiding a leg on a palpable error, differing rules on how a suspended game settles, and limits that stop you staking the amount the split requires.
Is arbitrage the same as positive EV betting?
No. An arb locks a small profit by covering every outcome and requires two accounts and precise timing. Positive EV betting takes one side at a price better than fair value and accepts that individual wagers lose regularly, with the advantage showing up over a long run. Arbitrage is about a certain small return, and positive EV is about a favorable average.
Every book, one screen
Price differences between books are the starting point for any value-based approach. Our odds board puts them side by side across the sports and markets we cover.