Also called: accumulator, acca, multi.
A single bet combining several selections, all of which must win. The payouts look large because the fee compounds with each leg, not because the book is being generous.
A parlay combines two or more individual bets, called legs, into one ticket. Every leg has to win for the ticket to pay. If one leg loses, the whole parlay loses. If a leg pushes, most sportsbooks remove that leg and recalculate the ticket using the remaining selections. A voided leg is handled similarly, although house rules can vary.
For example, a three-leg football parlay might include one team to win, another team to cover the spread, and a game total to go over. The payout is based on all three prices multiplied together. That all-or-nothing condition is why the potential return looks much larger than placing the same bets one at a time.
A bigger possible payout does not automatically mean a better price. Each leg already includes the sportsbook's fee, often called vig or hold. Combining legs compounds that cost. The more legs added, the more ways there are for a ticket to lose and the more important it is to compare the offered payout with the fair probability of every outcome.
A simple way to think about it is to convert each price to implied probability, then multiply the probabilities for independent legs. That produces an estimate of the chance that all legs win. Comparing that probability with the ticket's payout helps separate a genuinely competitive price from a flashy number that does not justify the risk.
Legs are correlated when one outcome makes another more or less likely. A quarterback passing for a large total and that quarterback's team winning are a common same-game example. Sportsbooks account for correlation in same-game parlays by changing the price or restricting combinations, so multiplying the standalone odds is not a reliable way to price those tickets.
Independent legs are different: the result of one should not alter the chance of the other. Before treating a parlay as independent, check whether the same weather, player availability, game script, or matchup assumption affects more than one selection. If it does, a fair price needs to reflect that connection.
Start by checking each leg as a standalone bet. If a leg is not worth taking on its own price, adding it to a parlay rarely improves the decision. Then compare the total ticket price across available books, especially for same-game combinations where each book can model correlation differently.
Keep the stake sized for the chance that every leg needs to win, rather than for the advertised payout. A record of the price taken, the line, and the closing line makes it easier to review whether selections were priced well over time. VigWatch's parlay lesson explains the calculations in more detail, while the calculators collect the odds and probability tools needed to check a ticket.
See also: Leg, Same-game parlay, Correlation, Round robin, Straight bet