An accumulator is a type of bet that incorporates multiple selections in one single wager. In a win four-fold accumulator, a customer would make four selections and all selections in the accumulator would have to be successful in order to win the bet. Odds are given by multiplying the odds of each selection by the following selection.
For example, if a customer puts four 3/1 shots in their accumulator, their odds of winning the bet would be 255/1. This is calculated by multiplying the stake and return of the first selection, which would be four, by the second, third, and fourth selections (4 x 4 x 4 x 4 = 256). The stake is included in the returns, so when the stake is removed the odds return at 255/1. The more selections that are made, the bigger a bookmaker’s over-round becomes. This is why you may see bookmakers offering bonuses on accumulators.
Accumulators can come in various shapes and sizes. A punter may just want to make two selections. This is known as a double, with three selections known as a treble. Accumulators can also be played each-way, a popular bet in horse racing. If a customer places an each-way treble, they effectively place two bets: one for the three horses to win and one for the three horses to place. If two win and one places, only the place half of the bet is landed. If two win and the other horse loses, both parts of the bet lose. Trixies, Yankees and Heinz bets are a selection of different accumulators combined under one term. For example, a trixie requires three selections and is a four-bet accumulator consisting of three doubles and one treble.
Bookmakers forbid two markets from the same event being used in an accumulator. For example, betting on Manchester United to win 2-0 and combining that with there to be under three goals in the match would be a conflict. The odds are already accounting for there being fewer than two goals in the game in the price of the first selection.
A gentleman in the UK managed to place an accumulator bet in a popular high-street bookmaker in 2010 without realising that his bets conflicted. He was due to win £7,000,000 from a £5 stake. He bet on the popular “Will it snow on Christmas Day market” but he combined several towns across the country in his bet. The weather is an obvious conflict; if it’s due to snow in one town, it’s very likely it will snow in several other towns nearby and the odds of it snowing across several parts of the country on Christmas Day do not equate to somewhere in the region of 1,000,000/1. The bookmaker apologised for their member of staff taking the bet in error and paid the customer £31, the total he would have returned if splitting his stake across single bets.