Definition
A surebet (also called a sure bet or sports arbitrage) is a set of bets, placed with different bookmakers, that covers every possible outcome of an event and returns more than the total stake whichever outcome wins. The profit comes from the bookmakers disagreeing, not from predicting the result.
The condition
Take the best odds on offer for each outcome and convert them to implied probabilities (1 / decimal odds). If they add up to less than 100%, a surebet exists. Example for a two-way market: odds of 2.10 on one side (47.6%) and 2.15 on the other (46.5%) add up to 94.1%, so staking in proportion locks in about 6% of the total stake.
How it maps to prediction markets
A binary prediction market is a two-outcome surebet where each side pays $1.00 if it wins. YES at $0.46 on one platform and NO at $0.52 on another cost $0.98 together and pay $1.00 either way. This is complement arbitrage, one form of cross-market arbitrage.
Why surebets are harder than they look
- They close fast. Odds and prices update within seconds, so a slow second leg can leave you with one open bet. See two-leg execution.
- Rules must match. Both bets need the same settlement rules, or the "sure" outcome isn't sure. See resolution risk.
- Fees and limits apply. Commissions, stake limits and account restrictions at bookmakers shrink or block the gap.