Calculate stakes, profits, and ROI for surebets, middles, and lay bets. Supports Asian Handicap, quarter lines, and exchange commission.
A surebet (or arb) is when you bet on all outcomes of an event across different bookmakers, exploiting odds differences to guarantee a profit regardless of the result. If the combined implied probabilities are below 100%, you have an arb. The calculator shows optimal stake distribution and your guaranteed ROI.
A middle is a special type of arb where overlapping lines mean a specific result can win both bets. For example, Over 2.5 at one bookmaker and Under 3 at another. If exactly 3 goals are scored, both bets win. Middles guarantee a small profit on most outcomes with a bonus payout if the result lands in the gap. The calculator tests every possible outcome and shows your profit window.
A back bet is the standard type of bet most people are familiar with. You are betting on something to happen — for example, backing Team A to win a match. If Team A wins, you receive your stake multiplied by the odds. If they lose, you lose your stake. Every bet you place at a traditional bookmaker (Bet365, Paddy Power, William Hill, etc.) is a back bet.
A lay bet is the opposite of a back bet. You are betting against an outcome — for example, laying Team A means you win if Team A does not win (draw or Team B win). Lay bets can only be placed on a betting exchange, not at a traditional bookmaker. When you lay a bet, you take on the role of the bookmaker: if the outcome happens, you pay the backer their winnings (your liability). If it doesn't happen, you keep their stake minus commission.
Lay bets are used in matched betting, qualifying bets, and free bet extraction. By combining a back bet at a bookmaker with a lay bet on an exchange, you can cover both sides of an event and guarantee a specific outcome regardless of the result.
A sportsbook (bookmaker) sets its own odds, takes your bet, and pays you if you win. The bookmaker is always the counterparty — you are betting against the house. They build a margin (overround) into their odds to guarantee themselves a profit over time.
A betting exchange (Betfair, Smarkets, Orbit Exchange) is a marketplace where bettors bet against each other. The exchange does not set odds — users offer and accept odds. Because there is no bookmaker margin, exchange odds are usually sharper (closer to the true probability). The exchange charges a small commission (typically 2–5%) on winnings instead.
Exchanges are essential for arbing because they allow you to lay bets (bet against an outcome), which is not possible at a traditional bookmaker. They are also where the sharpest odds are found, making them a key component of value betting strategies.