The traditional answer to this question is 4.5%. That's the bookmaker’s edge on a bet that has a 50/50 chance of winning, where the bookmaker charges the conventional "vig" (short for "vigorish," meaning "a charge paid on a bet") of -110 on each side (i.e., bet $110 to win $100). Considering the multiple betting options available, however, as well as the way sports books have extended their presence into new places like the Internet, the answer becomes more complex.
The most common bet for people to make at a Las Vegas sports book would be either a side or a total. A side is where you pick one team, plus or minus points, versus the other team. Betting on the total means wagering that the total points for the game will be over or under the sports book's posted number. Most people bet this at -110, giving the above 4.5% edge to the house.
Proposition ("prop") and futures bets often vary from the standard -110, however. They tend to include a greater house edge because the bookie feels less confident in making a good line on these. A prop bet may offer -115 on each side or even -120, for example, which increases the house edge to 6.7% or 9%, respectively.
One way to cut down the house edge is to shop for the best line. This means getting the most points if you’re betting the underdog and laying the fewest if you’re betting on the favorite. For example, if four sports books are offering your team +4 points and a fifth casino is offering +4.5, take the +4.5 because this means you’ll win instead of pushing if your team loses by exactly four points.
These days, the Internet offers significant value for bettors. There are new "low vig" books that use a reduced house edge as their primary selling point to acquire and keep customers.
Hollywood Sportsbook, for example, is an example of a low-vig book. They offer -107 betting instead of -110. This lowers the house edge to 3.15%.
The lowest-vig betting that we're familiar with is dealt at Pinnacle Sports. They offer -104 betting on NFL sides, thus reducing the house edge to 1.8%. There are few sports books that could afford to stay in business with an edge this small, but Pinnacle, as a result of their value, gets enormous volume, which makes it viable. Huge betting volume combined with a 1.8% edge gives them a profitable system. Pinnacle also offers -105 betting (2.2% house edge) on NFL totals, NBA sides and totals, and other major sports.
Anthony Curtis, in his now out-of-print book, Bargain City, wrote that he believed betting on sports to be one of the best gambling values in a casino. This is because of the low house edge combined with the time factor. Certain games like blackjack, craps, and baccarat have a lower house edge than a sports bet. The difference, however, is that those games are played much faster. You may have 100 decisions (hands, rolls, etc.) an hour in those games, while with a sports bet you'll have one decision every three hours or so. Take this example:
If you bet $11 to win $10 on an NFL team, your expected loss is 4.5%. So it's like getting three hours of entertainment for about 50 cents (4.5% x $11). You may even get a free drink ticket when you place your bet (gotta ask for it!), which actually makes you a net winner on the proposition.
