TERM
Surebet
Bets on every outcome of an event at different bookmakers where the sum of inverse odds is below one, so the payout beats the total stake whatever happens.
A surebet (also called an arb or arbitrage opportunity) exists when 1/k₁ + 1/k₂ < 1 for two outcomes or 1/k₁ + 1/k₂ + 1/k₃ < 1 for three. Stakes are split in proportion to the inverse odds, so the payout is the same whichever outcome happens. A surebet's return is called ROI.
Surebets arise when two bookmakers price an event differently and when a book is slow to update its live line. According to Dozor data for September 6, 2026, the median surebet lifetime is 2.1 seconds, and 5% last longer than a minute. A walkthrough with a worked example is in the article “What Is a Surebet in Betting and How to Calculate It”; to calculate stakes, use the calculator.