The bookmaker's margin, explained with one coin toss

Imagine a bookmaker taking bets on a fair coin. True odds are 2.00 on each side, but no bookmaker offers that; you'll see something like 1.91 and 1.91. Convert to implied probability and the two sides sum to about 104.7% — the extra 4.7% is the margin, the price of the service.

Every market works the same way. The margin varies by sport, competition and operator — headline football markets might carry 2-5%, obscure markets much more — and it's the main honest way to compare value between bookmakers.

This is also the arithmetic behind 'the house always wins in the long run'. The margin doesn't make any single bet a loser, but across thousands of bets it grinds in the operator's favour, which is why betting is entertainment with a cost, not an income strategy.

Knowing the margin doesn't beat it. It just tells you exactly what the entertainment costs — and comparing that cost is precisely the kind of dull, useful work this site is for.

As with everything on this site: the operators reviewed here are licensed, the facts carry the date we verified them, and none of this is a prediction or a promise. Bet with money you can afford to lose, or don't bet at all — both are respectable choices.