What is a bookmaker margin and why does it affect my winnings?

A bookmaker margin (also called the overround or vig) is the built-in profit percentage a bookmaker embeds into its odds. It means the total implied probability of all outcomes in a market adds up to more than 100%.

Are betting exchanges always better value than traditional bookmakers?

In the vast majority of cases, yes — betting exchanges offer better value than traditional bookmakers because they replace the hidden margin with a transparent commission structure.

How do I calculate the margin on a set of odds?

To calculate the margin on any market, convert each outcome's decimal odds into an implied probability by dividing 1 by the decimal odds. Then add all implied probabilities together.

Which sports typically have the lowest bookmaker margins in the UK?

Premier League football match result markets, major horse racing meetings, ATP and WTA Grand Slam tennis, and major boxing and MMA events typically feature among the tightest-margined markets.

Can I trust low-margin betting sites that are not well-known brands?

The most important thing to check with any bookmaker is whether they hold a valid UK Gambling Commission (UKGC) licence.

What is Best Odds Guaranteed and how does it help reduce the effective margin I face on horse racing?

Best Odds Guaranteed (BOG) is a promotion offered by many UK bookmakers on horse racing. When you take an early price on a horse and the official starting price turns out to be higher, the bookmaker will pay you at the higher SP.

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Last Updated: 2026

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