A bookmaker sets the price and takes your bet. An exchange is a marketplace where punters bet against each other. The difference is why exchange prices matter.
At a bookmaker, the bookmaker is your opponent: it sets the price and takes the other side. On an exchange, another punter takes the other side. The exchange just matches the two of you and charges a small commission on winnings, typically a few percent.
Betfair is the biggest. Smarkets and Matchbook work the same way.
Backing a horse is betting it wins. That is the only bet a bookmaker offers.
On an exchange you can also lay: bet that a horse loses, playing the bookmaker's side. Every matched bet is one punter backing and another laying the same price.
A bookmaker's price has margin built in. An exchange price is where real money agrees to trade, with no margin. That makes it the best public estimate of a horse's true chance.
Exchanges also price the win and the place as separate markets. That is what makes the place part of an each‑way bet checkable: the exchange says what the place is really worth.
When a bookie's price beats the exchange, that is an arb: value confirmed by a live market. How each‑way arbing works.
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