Betting
That difference — roughly 10 per cent on the individual horse racing betting sites not on gamstop price — is the cost of the bookmaker margin. One person backs a horse to win; another lays it (bets against it winning). The betting exchange — Betfair being the dominant platform — operates on a fundamentally different model to a traditional bookmaker. Among fixed-odds bookmakers, bet365, Paddy Power, and William Hill tend to be competitive on feature races, while some smaller operators run wider books, particularly on less prominent meetings. By the time the race starts, competition among operators has usually tightened the market.
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The overround on the Grand National ante-post market can reach as high as 180 per cent — a level that would be considered predatory in any raceday market. It varies by operator, by race type, and by the time of day. If Bookmaker A is running a 115 per cent book on a race and Bookmaker B is running a 125 per cent book, Bookmaker A is systematically offering better value across the entire field.
Around major meetings — Cheltenham, the Grand National, Royal Ascot — bookmakers offer boosted prices on selected runners. If the exchange offers 6.0 and the bookmaker offers 5/1, the bookmaker is competitive after commission. Instead of setting odds and accepting bets against them, the exchange matches punters on opposite sides of a bet. At the upper end, you find big-field handicaps with 20 or more runners, where each horse price can be inflated by a few ticks without any individual punter noticing the difference.
The practical approach for most punters is to use both. If you back at 6.0 (5/1) and pay 5 per cent commission on your winnings, your effective odds are 5.75 (approximately 19/4). On a Monday afternoon novice hurdle at a minor track, liquidity is thin. Over time, backing at exchange odds rather than bookmaker odds produces a measurably higher return on investment, assuming you can find liquidity on your chosen market. The exchange takes a commission on the net winnings of the winning side, typically between 2 and 5 per cent depending on the user’s activity level.
When bookmakers extend place terms on big handicaps — paying five or six places instead of four — they compensate by widening the margin on the place element of each-way bets. At the lower end, you find small-field Flat races — Group 1 contests with five or six runners where the form is well established and bookmakers compete aggressively on the headline price of the favourite. The difference between 3/1 and 7/2 is not dramatic on a single bet, but across 200 bets over a season it represents dozens of units of profit or loss. Checking the overround before you bet is not something most punters do, but it takes less than a minute with a calculator or an odds comparison site. Small-field races with well-fancied favourites tend to carry lower overrounds (closer to 110 per cent) because the market is more efficient and bookmakers compete harder on the headline price of the favourite.
The overround is 5.9 per cent, meaning the bookmaker has built a theoretical edge of just under 6 per cent into the market. It is the bookmaker’s theoretical profit margin before a single bet is settled. In practice, they always sum to more — typically between 110 and 130 per cent for horse racing — and that excess is the overround.
The individual difference may be small — perhaps 5/1 versus 11/2 — but across hundreds of bets over a year, that cumulative margin is the difference between a profitable punter and a losing one. The take varies from state to state and the money is used to pay taxes, purse money for the horsemen, expenses at the track, and the track’s profit. If the exchange is at 7.0 and the bookmaker is at 6/1, the prices are closer, and after exchange commission the bookmaker might even be marginally better. Oddschecker is the most widely used in the UK and shows prices from all major bookmakers side by side, updated in near-real time. If the exchange offers 7.0 and the bookmaker offers 5/1, the bookmaker is taking a significantly larger margin on that runner, and you should either back on the exchange or find a bookmaker whose price is closer to the exchange level. On short-priced selections — odds-on or evens — the exchange commission can actually make the bookmaker price competitive or even better, because the commission is a fixed percentage of the profit regardless of the odds.
