In the parlance of gambling, to “parlay” a bet means to risk a stake plus its winnings in successive wagers. For example, bet £2 on Arsenal at evens this week, and if they win parlay the original £2 plus the £2 profit on the Gunners again the following week for a total stake of £4. If they succeed again, parlay the bet by putting all £8 on them in the third week. Should they accomplish the hat trick, collect £16 for what was originally a £2 bet.
This type of parlay works quite nicely when the selections made are independent events and separated by sufficient time to collect winnings and make the next wager. However, such betting is not possible in cases where contests are being conducted simultaneously (e.g., three football matches on the same afternoon) or multiple bets are made on a single event (e.g., total score over/under, first goal scorer, team to win, etc.).
To remedy this situation, bookmakers introduced an alternative form of “parlay betting,” with selections treated as a group and only a single wager required instead of a succession of re-bets. Special odds are offered, depending on the number of selections. For example, in the case of all selections made at evens, the following parlay odds would apply, along with the true odds that would accrue if the bets could be made in succession:
Obviously, the bookmakers have created some substantial margins for themselves. In order for the bettor to win and claim a return, all of the selections must succeed. If even a single selection fails, the entire stake is lost.
There is effectively no difference between parlay betting and the wager known as an “accumulator” bet other than the odds paid. Accumulator odds are typically calculated as a product of the individual odds on each selection. Parlay odds are most often based on “spreads” so that each selection can be offered at even money.
One interesting variation on parlay betting is the “progressive parlay,” which allows some losses among the selections bet upon and the wager still pays out as a winner. The following chart serves an example:
# of Plays All Win 1 Loss 2 Losses 3 Losses
4 5-1 1-1 -- --
5 11-1 2-1 -- --
6 20-1 9-2 -- --
7 40-1 4-1 1-2 --
8 75-1 10-1 2-1 --
9 150-1 20-1 5-2 --
10 250-1 25-1 3-1 1-1
11 400-1 60-1 5-1 1-1
12 900-1 80-1 10-1 3-1
Not all bookmakers offer progressive parlays, and those that do may limit them to certain major events. Again, the bookmakers have designed high margins into the odds paid on such parlay betting versus the true odds, but the advantage to the bettor is that if the very first selection fails, the entire wager is not automatically lost.
One concern of both bettors and bookmakers is what happens in the event of a draw. Terms and conditions must be clearly spelled out to protect both parties. In some cases, a “must win” rule may apply and the entire parlay bet will be deemed a loser in the event of a single draw.
In other cases, the wager may be reduced by one selection, so that a four-selection parlay bet becomes three selections and is rewarded accordingly. Some bookmakers have also introduced “ties win” parlay betting at reduced odds, while others offer “half-point” spreads so that no selection can result in a draw.