What is Arb / Arbitrage?

Arbitrage betting (arbing) exploits differences in odds between bookmakers to lock in a profit regardless of the outcome. By staking proportionally on all possible results at different sportsbooks, the bettor guarantees the same return whichever way the event goes, capturing the gap between the prices as a small but certain margin. The mechanics rest on the arbitrage percentage: add up 1 divided by each decimal price. A total below 100% means a guaranteed profit equal to the shortfall. Worked example: Bookmaker A offers 2.10 on Team A; Bookmaker B offers 2.10 on Team B. The two implied probabilities are 1/2.10 + 1/2.10 = 0.952, leaving a 4.8% margin. A total stake of £200 split £100 and £100 returns £210 either way — a guaranteed £10 profit on £200 risked, about 5%. When the prices differ you stake in inverse proportion to the odds so each outcome yields an identical payout. Why it matters: an arb is a rare instance of mathematically certain profit in betting. The catch is that margins are slim, so meaningful returns require sizeable bankrolls and rapid placement before prices shift. Common caveats: arbing is legal but heavily disliked by bookmakers, who will limit or close accounts they suspect of it, sometimes within days. Execution risk is real — odds can move between placing your two legs, and a voided or cancelled bet leaves you with an unhedged exposure. Specialist software such as OddsJam and RebelBetting scans markets to surface arbs and calculate stakes, but the operational risk of restriction remains. Treat arbing as a discipline in execution and bankroll management, not free money. Compare to: Arbitrage, Value Bet, Vig.