Correlated parlays are a dream concept for sports bettors – in some cases they have a positive long term expectation. In other words, if you bet these bets time and time and time again then you would make a guaranteed profit. they are like a guaranteed cash machine. Of course, virtually everything that seems too good to be true is, so finding and betting these parlays is very difficult. Before we get too much into that, though, let’s understand what we are talking about.

Simply put, we are talking about situations in which if one thing happens then another thing is very likely to happen as well. The simplest example is using football. If the total in a game is 45 and one team is favored by 30 points then it stands to reason that if the favorite covers the spread there is a better than average chance that the game will go over as well. Those two outcomes would be correlated.

So, how does that translate to long term profit? That requires some simple math. In a two event parlay there are four possible combinations – you win both games, you lose both games, you win the first and lose the second, and you lose the first and win the second. If the point spreads are set reasonably well then in each game there should be about an even chance of ending up on either side of the spread. That means that the likelihood of each one of those four possible outcomes is basically the same – 25 percent. That in turn means that in order for you to break even betting any one of those combinations over the long term you would need odds of 3/1 – and better than that to show a profit. Since two teams parlays typically pay off at about 2.6/1 parlays are typically not a great bet because of their negative expectation – you are losing money in the long term even when you win a parlay bet. When two events are correlated, though, then the percentages change. Let’s say that in our original example the chances of winding up on either side of the 30 point spread is the same. If the favorite covers, though, then it is going to go over the total much more often than it goes under – because the favorite has to cover at least 31 points to cover, so there aren’t that many scores that will allow the favorite to cover and the game to still go under the total. We could say, then, that if the favorite covers there is an 80 percent chance that the game will go over, and a 20 percent chance that it will go over. Overall, then, that means that there is a 40 percent chance that the game will go over and the favorite will cover. That means that 40 percent of the time you parlay the favorite and the over you are going to win. If you made a $100 parlay bet 10 times then you would expect to win four times with a total profit on those wins of $1040. The six losses would cost you a total of $600. That means your profit would be $440.

It sounds great, but the problem is that sports books really hate losing money, so they make it very hard to make bets like this. Several books have gone to the extreme of not allowing you to parlay two events in the same game at all. Others will let you parlay one game, but will reject the bet (when it is placed or even after the game) if it turns out to be correlated. There is a general rule you can use to tell if something is likely to be viewed as correlated – if you multiply the point spread by three and the result is larger than the point spread then the two events will likely be viewed as correlated. That means that in that game you likely won’t be able to parlay the over and the favorite or the under and the underdog.

While the likelihood of finding directly correlated parlays that you can bet is low these days the principles behind them can still be applied in situations that can have the same basic effect. If, for example, you can find situations in two different games that are closely related then you could have an attractive situation. The classic example is two teams playing their last games of the season with a playoff spot on the line for one of those teams. Let’s say the Patriots play at 1:00, and the Jets play at 4:30. If the Patriots win then they get the playoff spot, and the Jets are eliminated. If the Patriots lose, though, then the Jets can earn the playoff spot with a win. If the Pats win then the Jets will have nothing to play for, they aren’t going to play hard, and they might not even play their starters. That could make it harder for them to win or cover. On the other hand, if the Patriots lose then the Jets are likely to play especially hard and will be highly motivated. that means that they are perhaps likelier than normal to win and, depending on the spread, cover. You could find in those situations that the parlays of those two situations – a Pats win and a Jets loss, and a Pats loss and a Jets win – would be correlated. That would be a bet you would definitely be able to make.