Accumulator Bets Explained: How Accas, Parlays and Round Robins Work

An accumulator bet (an acca, called a parlay in the US and an express bet on some sites) combines several selections from different events on one bet slip. The odds of the selections are multiplied into one price, and the bet only wins if every selection wins. This guide works through a real three-selection slip, shows what happens when a match is postponed, and explains system bets, which US sportsbooks call round robins.

What is an accumulator bet?

A single bet is one selection on one event, paid at stake × odds if it wins. An accumulator joins several of them:

• Double, treble, fourfold… describe the number of selections. A treble is three selections on three different events.
• The slip’s odds are the product of the selections’ odds. Selections at 1.435, 1.63 and 1.51 give combined odds of 3.532.
• One losing leg loses the whole bet. In 22bet’s rules: “Should at least one leg fail, the whole bet is lost.”
• No related outcomes. Two selections where one affects the other (for example two markets on the same match) cannot sit in one accumulator; if they do, 22bet removes the one with the lowest odds.

Any market can be a leg: 1X2, Asian handicap, goal totals or corners, and different sports can be mixed on the same slip.

How accumulator odds are calculated: a treble

Three selections at the prices 22bet offered for matches on 17 October 2026:

A 100,000 VND treble returns 100,000 × 3.532 = 353,197 VND if all three win, stake included. Three separate 100,000 VND singles cost 300,000 VND and return 143,500 + 163,000 + 151,000 = 457,500 VND if all three win, but the singles still return something when only one or two win; the treble does not.

What happens if a match is postponed or void?

A void leg does not void the whole accumulator. Under 22bet’s rules:

• A pre-match event postponed by more than 48 hours is void. Inside an accumulator the void leg is settled at odds of 1 and the remaining legs stand.
• A bet accepted after an event has started (other than in-play) is settled at odds of 1, and so is that leg inside an accumulator.
• If every leg is void, the stake is returned.
• A whole-number line that lands exactly (a total of 2 goals, a handicap of 0 that ends level) is refunded, so that leg also counts at 1.

How fast accumulator odds grow

The table assumes every selection is priced at 1.50 and has a 60% chance of winning:

Odds and probability are both multiplied leg by leg, so each extra selection raises the potential return and lowers the chance of the whole slip landing at the same rate.

The bookmaker’s margin multiplies the same way. In the treble above, the Betis v Barcelona 1X2 market carries about 5.5%, Bologna v Inter about 5.3% and the Brentford v Liverpool 2.5 goals line about 8.8%; multiplied together the margin on the treble is about 17%. How to work out a margin is on the house edge page.

System bets and round robins

A system bet splits one stake into several smaller accumulators from the same group of selections, so it can pay without every leg winning. US sportsbooks call the same thing a round robin: a “round robin by 2s” on three selections is a 2/3 system, three doubles. With 60,000 VND on the treble above, each double carries 20,000 VND:

The number of accumulators grows quickly: a 3/6 system is 20 trebles, a 4/8 system is 70 fourfolds. 22bet allows up to 20 selections and up to 184,756 accumulators in one system. Other combination bets in 22bet’s rules:

• Lucky: 2 to 8 selections, made up of every single and every accumulator they form; four selections make 15 bets (the same structure as a Lucky 15). It pays if at least one selection wins.
• Patent (22bet’s definition): 3 to 8 selections, every accumulator of two or more legs and no singles; four selections make 11 bets. At least two selections must win to get a return.
• Chain: a series of singles in an order you choose, where each return funds the next stake.
• Anti-accumulator: the reverse of an accumulator, which wins if at least one selection loses.

Cashing out an accumulator

22bet’s bet slip sale lets you sell an accumulator back, in full or in part, at the price the bookmaker offers while the matches are still running. The sale option disappears once the result of any match on the slip is settled. How the price moves and how Auto Sale works is covered in the in-play betting guide.

Where to place accumulator bets

22bet accepts accumulators on pre-match and in-play markets, and its promotions page carries a daily accumulator section (ready-made accumulators on the day’s main matches) and a Bet Booster offer for accumulators. The 22bet sports welcome, 100% of the first deposit up to 3,172,000 VND, is itself wagered on accumulators: 5 times within 7 days, on accumulators of 3 or more selections with at least 3 of them at odds of 1.40 or higher. The treble in the example above (1.435, 1.63, 1.51) meets that condition. Read the full 22bet review, compare sportsbooks on our betting sites page, or see how odds formats convert in Asian odds explained.

A common leg in football accumulators is both teams to score; its league-by-league rates are on that page.

Bet responsibly

The longer the accumulator, the bigger the potential return and the smaller the chance that every leg wins, and the bookmaker’s margin builds up with each selection. Only stake what you can afford to lose, set a limit before each round of fixtures, and never chase losses. Betting is for adults 18+ only.