Accumulator
A single bet that links several selections together, where every selection must win for the bet to pay out.
Definition
An accumulator combines two or more selections into one wager, multiplying their odds together so a small stake can return a large amount. Because the return from each leg rolls into the next, potential winnings grow quickly — but the entire stake is lost if even one selection fails. That same compounding also stacks the bookmaker's margin across every leg, making accumulators one of the higher-edge products in sports betting. The term is standard in the UK and Europe ("acca"); the equivalent bet is called a "parlay" in North America and a "multi" in Australia.
Worked example
A bettor places a £10 four-fold accumulator on four football matches at decimal odds of 1.50, 2.00, 1.80 and 2.50. Multiplying these gives combined odds of 13.50 (1.50 × 2.00 × 1.80 × 2.50), so all four winning would return £135 — a £125 profit on the £10 stake. If any single match fails to land, the full £10 is lost, regardless of how the other three perform.
Why it matters
Accumulators are among the most heavily promoted sports-betting products because a low stake advertises a large headline return — yet each added leg both lowers the real probability of winning and compounds the operator's built-in margin, so the effective house edge is considerably higher than on a single bet. For learners, the acca is a clear illustration of how odds multiply and why "more selections" means more risk rather than better value. For professionals in trading, marketing or player protection, it is a central example of where the entertainment framing of a product diverges from its mathematical reality.
Related
Note: Core definition is stable. Terminology is regional (acca in the UK/Ireland, parlay in the US/Canada, multi in Australia). Settlement of a void or postponed leg varies by operator — typically the selection is removed and the accumulator recalculated on the remaining legs — as do add-ons such as acca insurance, accumulator bonuses, and same-game multis (bet builders) that permit correlated selections. Minimum leg counts and the fold naming (double, treble, four-fold) also vary by operator; verify specifics against the relevant operator's rules.