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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. In a perfectly fair market with no margin, the implied probabilities of all runners in a race would sum to exactly 100 per cent. Understanding those differences is where value lives. The bookmaker margin is built into every price, but how wide that margin is varies enormously between operators, between race types, and between the fixed-odds market and the betting exchange. Yet the majority of bettors place their bets with whichever app they last used, at whatever price happens to be on screen, without checking whether a better number is available elsewhere.
On horses that drift — less money than expected, price lengthening — BOG gives you the benefit of the higher SP. On horses that are supported in the market — money coming in, price shortening — BOG adds nothing, because the SP is lower than the price you took. Check the exchange price on your selection before placing with a bookmaker.
But the punter who simply opens an account with one bookmaker and accepts whatever price they see is leaving money on the table. Bookmakers are fighting for your custom with promotions like Best Odds Guaranteed, enhanced place terms, and competitive pricing. Horse racing punters, in other words, are moving serious money through these markets, and the opportunities for finding value in UK racing have never been more varied.
The difference between 5/1 and 6/1 on the same horse in the same race is a 20 per cent increase in profit — free money, essentially, for the 30 seconds it takes to check a second bookmaker. Each-way is unprofitable on short-priced horses where place returns are minimal, in small fields with weak terms, and when your assessment favours win-or-nothing outcomes. BOG value emerges when horses attract late support and steam into shorter prices, while your early-morning selection drifts in consequence. Always check the specific terms at your chosen bookmaker before calculating whether each-way represents value. For punters betting on the morning’s early races or taking ante-post positions that settle on the day, checking the activation window is essential.
Flutter Entertainment, which owns Betfair, reported global revenue of $14 billion in 2024 across 13.9 million average monthly users, but the exchange is only one part of that portfolio, and liquidity varies enormously by market. On a Monday afternoon novice hurdle at a minor track, liquidity is thin. On feature races — the Champion Hurdle, the Gold Cup, the Grand National, Saturday afternoon handicaps at major tracks — the exchange market is deep enough that you can back at the displayed price without difficulty. 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. Where a bookmaker might offer 5/1 on a horse with a 120 per cent book, the exchange might show 5.5 (or 9/2 in fractional terms) on the same runner with a total market overround of 103 per cent.
Using the exchange as a benchmark — even if you ultimately bet with a bookmaker — is one of the most effective habits a punter can develop. 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 betting places not on gamstop or find a bookmaker whose price is closer to the exchange level. If the exchange offers 6.0 and the bookmaker offers 5/1, the bookmaker is competitive after commission.
Oddschecker is the most widely used in the UK and shows prices from all major bookmakers side by side, updated in near-real time. Despite these caps, BOG remains the single most consistently valuable promotion in horse racing. And some operators apply BOG only to bets placed after a certain time in the morning, which means very early ante-post-style wagers do not qualify. There are practical considerations that limit BOG value.
That difference — roughly 10 per cent on the individual price — is the cost of the bookmaker margin. 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. Instead of setting odds and accepting bets against them, the exchange matches punters on opposite sides of a bet. The betting exchange — Betfair being the dominant platform — operates on a fundamentally different model to a traditional bookmaker.
Then let the market move as it will—your downside is protected, and any drift converts into bonus profit. Strategic use of BOG requires understanding when to bet and when to wait. This promotion exists because bookmakers are competing for early-morning turnover. A six-runner race where implied probabilities sum to 112% has a 12% overround—meaning the bookmaker’s theoretical margin is 12% before any punter places a bet. But without calculating implied probability, you cannot begin to answer that question systematically.
