How to find arbitrage bets

You find an arbitrage bet by taking the best available price on every outcome of a market, across all the books you can bet at, and converting each to its implied probability. If those probabilities add up to less than 100%, you can back every outcome and get back more than you staked whichever one happens. To size it, stake each outcome in proportion to its implied probability. The rest of this guide is why the gap appears, the arithmetic for spotting and sizing one, and why nobody finds them by hand for long. For what an arb is and how to place one safely, start with the arbitrage guide.

Why books disagree at all

Each sportsbook sets and moves its own prices. Some copy the sharp market closely and move within seconds; others update slowly, shade prices toward what their own customers bet, or post a number and leave it. When news breaks or money hits one side, the books move at different speeds, and for a while one book can be offering the Over at a price that no longer matches another book's Under. Each book's own market still has a margin in it — see hold and vig — but you are not betting one book's market. You are taking the best side from each.

Spotting one: add up the implied probabilities

Implied probability is the break-even win rate a price represents. For negative American odds it is odds ÷ (odds + 100) using the number without its minus sign; for positive odds it is 100 ÷ (odds + 100). In decimal odds it is simply 1 ÷ decimal. Add the figures for the best price on every outcome. Over 100% is a normal market with a margin in it; exactly 100% is fair; under 100% is an arbitrage, and 1 ÷ the total − 1 is the return on the whole position.

Sizing it: the stake-split formula

Pick the total you want to put into the position, T. The stake on each outcome is T × (that outcome's implied probability ÷ the total implied probability). Because each stake is proportional to 1 ÷ its decimal odds, stake × decimal odds comes out the same for every outcome, which is what makes the return identical. The same formula works for a three-way market; you just have three terms.

How long arbs last

Not long. The gap exists because one book has not caught up yet, and catching up is exactly what books are built to do. On popular pre-match markets they are usually gone within minutes, and in-play they can close in seconds. That is also why a 1.45% arb is typical and a 6% one deserves suspicion: a big gap is more often one book's error, and errors are the prices most likely to be voided — see arbitrage betting risks.

Why a scanner is necessary in practice

The arithmetic is easy; the search is not. Ten books, a ten-game NBA slate and forty markets per game is four hundred markets, each with ten prices per side, each able to change every few seconds. By the time you have checked one game by hand, the first price you wrote down may have moved. The arbs that exist are found by software that compares every book's price on every market continuously and flags the pairs that sum under 100%. Doing it manually mostly teaches you how rarely a gap survives the minute it takes to see it.

Where TrueEdge fits

The Arbitrage board runs that comparison across every book it prices and shows each live arb as a card: the return, each leg's price and book, linked stake boxes that re-split as you type, the payout line, when the pair was first detected, and a flag when one price looks like a mispricing. You can limit it to your own books and set a maximum quote age. The arbitrage walkthrough reads one card from top to bottom, and the Arb Stake Sizing calculator does the split for a pair you found yourself.