Arbitrage (Sure Bet) Calculator

What is Arbitrage Betting?

Arbitrage betting (also called sure betting or arbing) is a strategy that exploits differences in odds between bookmakers to guarantee a profit regardless of the outcome. When different bookmakers disagree enough on the probabilities of outcomes, a window opens where you can back every possible result and still come out ahead. The bookmakers are effectively subsidising your profit through their competing opinions. It is one of the only truly risk-free betting strategies that exists.

How Sure Bets Work

Consider a tennis match. Bookmaker A offers 2.15 on Player 1, while Bookmaker B offers 2.05 on Player 2. The sum of implied probabilities is 1/2.15 + 1/2.05 = 0.465 + 0.488 = 0.953, or 95.3%. Since this is below 100%, an arbitrage opportunity exists. By distributing your investment proportionally — more on the lower-odds outcome and less on the higher-odds outcome — you guarantee a return of approximately 4.9% on your total investment no matter who wins the match.

How to Calculate Arbitrage

The arbitrage percentage is calculated by summing the inverse of each decimal odds: Arb % = (1/Odds1 + 1/Odds2 + ...) x 100. If the result is below 100%, an arbitrage exists. The profit percentage equals (1 / sum_of_inverses - 1) x 100. To calculate the optimal stake for each outcome, multiply the total investment by each outcome's implied probability, then divide by the sum of all implied probabilities. This distributes your funds so every outcome returns exactly the same amount.

Is Arbitrage Betting Legal?

Yes, arbitrage betting is completely legal in most jurisdictions. You are simply placing bets with different bookmakers at the odds they freely offer. However, bookmakers actively dislike arbers because they cost them money. If a bookmaker identifies you as an arbitrage bettor, they may limit your stakes, restrict your account, or close it entirely. This is the main practical challenge: maintaining access to accounts across enough bookmakers to find and exploit arbitrage opportunities consistently.

Finding Arbitrage Opportunities

Manually comparing odds across dozens of bookmakers is impractical. Most serious arbers use dedicated odds comparison tools and alert services that scan hundreds of markets in real time and flag opportunities the moment they appear. Speed is critical because arbitrage windows often last only minutes or even seconds before the odds are corrected. Popular markets like football match results tend to have tighter odds, so look toward less-watched sports, lower leagues, and niche markets for the best arbitrage opportunities.