How does the number of decks affect house advantage?

By Alan Vaughn

You know what they say about dealers with big shoes… they have a large advantage. OK, so no one actually says that – but they should. It is a commonly accepted fact that the fewer decks in a blackjack shoe the more advantageous it is, but very few players know why.

There are several factors that work against the player as the number of decks increase, but deck size alone is often misleading when deciding on which games to play due to other factors.

When blackjack was first introduced, all of the games used one deck with rules similar to those of most six-deck games. These rules put the house at an advantage of less than .1% against the basic strategy player. With the invention of advantage play, casinos wanted to have a stronger advantage to protect themselves from players winning too easily at the tables. Their first attempt was to drastically change the rules of the game and continue using a single deck. This was obviously bad for players so even recreational players stopped playing and the casinos were forced to reconsider.

The casinos discovered in the process that increasing the number of decks resulted in the same increased advantage without the backlash from players. (Ironically, years later the invention of shoe games made casinos more vulnerable to advantage play.) The logic behind increasing the number of decks was based on the following three ideas: with more decks there are fewer stiff hands (12-16 in value); there are fewer blackjacks; and double downs are less powerful.

Fewer stiff hands may not sound like something that players want, but you need to remember that the pendulum swings both ways. Players have the option to stand or hit based on the value of the dealer’s up card. Dealers will be forced to draw in these situations, which will lead them to bust more frequently. The number of blackjacks also decreases slightly as the number of decks increase.

While this also decreases the frequency of dealer blackjacks, the player will suffer more due to the 3:2 payout. Probably the most significant advantage of fewer decks comes from the increased power of the double down. The reason that double downs decrease in value as the number of decks increase is that starting values of 9-11 all contain at least one small card (7 or lower) and frequently contain two small cards. These extra low cards mean that more high cards remain in the un-dealt portion of the deck. The effect of removing one or two low cards from a six-deck shoe is minimal, but the effect on a single- or double-deck game can be significant. With all of these changes considered, a six-deck game will have an extra .5% edge in favor of the house than a single-deck game with the same rules.

The extra advantage offered by single- and double-deck games only apply when the rules remain the same. In the current casino environment it is almost impossible to find a single- or double-deck game with the same rules as a six-deck game. Often the single- and double-deck games will have added restrictions on doubling, splitting and blackjack payouts that make them at best about equivalent to a generous six-deck game and at worst 3-4 times more costly.

The one rule that really increases the house edge is a 6:5 payout on blackjack. This may not look that different from 3:2 but it increases the casino advantage by about 1.4%. This additional edge causes you to lose 3-4 times as much in six-deck games, 5-6 times as much in double-deck games, and 100-200 times as much in single-deck games. Yes, that says 100 to 200 times as much.

While it is true that an increased number of decks is to the house advantage, that only holds true if all of the other rules remain the same. Depending on the location some players can still find a decent double-deck game, but single-deck games with favorable rules are quickly becoming extinct. As a player I try to bypass single- and double-deck games and look for a six-deck game with generous rules.

_ – Alan Vaughn has played high stakes blackjack for several years in casinos all across the U.S. He recently moved to Denver where he teaches blackjack to players of all skill levels. For questions, comments, or information on lessons please email denver21school@yahoo.com._