Accumulator (acca)

Four legs at 1.50, 2.00, 1.80 and 1.25 multiply to 6.75. A 10-unit stake returns 67.50 units if all four win, and nothing if any one loses. The combined price implies a 14.81% chance, which is the four legs' implied probabilities multiplied together.

Bookmaker margins compound the same way. Two legs at 1.90 on two-way markets combine to 3.61, where the same legs priced at evens would pay 4.00, so the margins cost the acca 9.75% of its price. Each extra leg multiplies in another margin, so a longer acca carries more of it.

A void leg, such as a postponed match, normally drops out and the acca settles on the legs that remain, though each bookmaker's rules decide. If the 1.25 leg above were void, the other three would settle at 6.75 ÷ 1.25, which is 5.40.

Acca promotions are a matched-betting target, from insurance that returns a stake when one leg loses to a boost on the combined price, and each bookmaker's own terms decide what qualifies. One way to cover an acca is to lay each leg separately on an exchange. Each leg's lay[] entry gives the lay price and available, the money that can be matched at it.

Legs often start at different times, and each event's commence_time puts them in order. A punter who lays as they go places each lay shortly before its leg starts, and only while the acca is still alive. That reduces the risk without removing it.

In the OddsRelay feed

An acca is priced from single prices, so a tool builds one from each leg's price at the bookmaker taking the bet. On OddsRelay's raw feed that is the bookmaker's entry in bookmakers[], then the leg's market and its outcomes[].price. On a matched feed back[] lists the bookmakers best price first, so the tool takes the entry for its bookmaker, which is not always the first.

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