Back & Lay: What a Betting Exchange Is

Bookmaker vs betting exchange

At a classic bookmaker, your opponent is the bookmaker itself: it sets the odds and keeps its margin. On an exchange, the platform simply connects players to each other — you request or offer an odd and someone else takes it. The exchange earns a small commission on net winnings, usually around 2%–5%.

Back: for an outcome

Back is what you already know: you bet that something will happen. Back €10 on Team A to win at odds of 2.50 → if it wins, you get €25 (€15 profit); if it loses, you lose your €10.

Lay: against an outcome

Lay is the reverse: you bet that something won't happen — you take the “bookmaker's” side against another player. You win their stake if the outcome doesn't happen, but you must cover their payout if it does. That risk amount is called liability.

Example: you lay €10 on Team A to win at odds of 3.0.

• If Team A does not win → you win €10 (your opponent's stake, minus commission).
• If Team A wins → you pay the liability: (3.0 − 1) × 10 = €20.

How this connects to arbitrage

Here's the magic: if you back an outcome at a bookmaker with high odds and lay the same outcome on the exchange at lower odds, you cover both sides with just two placements. When the back odds are high enough relative to the lay odds (after accounting for commission), you lock in guaranteed profit — that's “back/lay arbitrage”.

That's why ArbPlay doesn't only scan bookmakers but pairs them with betting exchanges for the lay leg — multiplying the sure opportunities that appear.

Don't forget commission

The exchange's commission reduces your net profit on the lay leg. An arbitrage that shows +1% before commission can become marginal after. Good arbitrage calculators (and ArbPlay) factor commission into the final percentage.

Related: What is arbitrage betting · How to calculate a sure bet · all guides.