What arbitrage betting is

An arbitrage, or arb, is when two sportsbooks disagree enough on a game that betting both sides pays you whoever wins. Each book sets its own prices. Most of the time they line up closely. Every so often they don’t, and that gap is the arb.

How to spot one

Turn each price into the chance it implies: 1 ÷ decimal odds. If the two chances add up to less than 100%, there’s an arb.

98.84% is under 100%, so betting both sides in the right amounts pays more than you put in.

How to size the bets

Split your total so both outcomes pay the same. With $1,000:

That profit is locked in only if both bets stand. The next section is about the times they don’t.

What goes wrong

Most guides stop at the math. These are the things that actually cost arbers money.

• The second price moves. Arbs close fast. If you place one side and the other price changes before you bet it, you’re holding a normal bet. Place the side most likely to move first, which is usually the price that’s out of line with the rest of the market.
• A book voids your bet. If a price was an obvious mistake, the book can cancel the bet. You’re left with only the other side.
• The two books settle differently. One book may void a player prop if the player doesn’t play while another grades it a loss. Baseball bets can depend on the listed pitchers. Check that both bets settle under the same rules.
• Your limits get cut. Books watch for arbing. Do it often and your maximum bet can drop to a few dollars.
• Odd amounts stand out. A $518.21 bet looks like a calculator made it. Round to the dollar: $482 and $518 still lock in at least $11.33.

Where arbs come from

• Books moving at different speeds. News breaks, one book updates in seconds and another takes a minute. That minute is where most arbs live.
• Promos. A profit boost or odds boost at one book can push its price past the rest of the market for that one bet.
• Sportsbooks against prediction markets. Kalshi and Polymarket prices are set by traders, not a trading desk, so they drift from sportsbook lines more often. Account for their fees before you count the profit.

A checklist before you bet

• Same game, same market, same line on both sides.
• Both bets settle under the same rules, including overtime and player participation.
• Both prices are still there right now. Refresh before the second bet.
• Your stakes are rounded and the worst case after rounding is still a profit.

Why the profit is small, and why people still do it

A typical arb pays 1% to 3% of what you put in. That adds up only with volume and a bankroll spread across several books. Most people get more out of the same skill by converting promos, like bonus bets and profit boosts, where the edge comes from the book.

Is arbitrage betting legal?

Betting both sides of a game at licensed sportsbooks isn’t against the law. Books are still allowed to limit or close your account under their terms, and many do once they spot it.

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