Learning how the number of blackjack decks changes the house advantage is essential if you want to turn blackjack into a positive expectation game. Whether you play using basic strategy or you're already an amateur card counter, understanding how the size of the shoe affects the house edge is key to going above and beyond the basics of blackjack math.
Strategy doesn't begin when you sit down at the blackjack table. The first step in a good blackjack strategy is walking through the casino doors and finding the right blackjack table. Every blackjack table in a casino is not the same. Being a good card counter and knowing proper blackjack strategy is not the only skill you have to learn. You'll also need to learn how to choose the right casino and the right table in that casino.
What Is Card Counting?
Counting cards is really just a system for figuring out how many of each card rank is in the deck relative to the total number of cards. Card counters keep track of those cards as they shift in and out of the deck. Skilled card counters know when to be aggressive based on the cards still in the shoe. If a casino only uses one deck at their blackjack tables, a card counter has an excellent chance of placing advantageous bets. If a casino uses 6 or 8 decks of cards in their blackjack shoe, the percentages don't move around as quickly and it is more difficult to know what cards are left in the shoe.
The best blackjack card counters know exactly how many decks a casino uses, how many hands are dealt before a reshuffle, and the specific rules a casino uses that alter the odds. Card counters also take note of how many blackjack players are at each table, because this affects the number of hands the counter will see per hour.
Number of Decks in Play
When card counters first started making their way into casinos, single deck shoes were far more common. Once casino managers got wind of the advantage that card counters held against them, they began to make small changes to shift the odds more in favor of the house. The quickest way to do this is to add more decks to the shoe. Nowadays, casinos offer blackjack games with up to 8 decks in a shoe. Single deck or two deck shoes tend to be extremely limited in terms of wagers, with max bets as low as $10.
But you don’t have to be a card counter to think about how the number of decks in a shoe affects blackjack strategy. A one-deck shoe is easier to develop basic blackjack strategy around. If you see two aces go out of that deck, it's pivotal information because there's only 4 of them to begin with. But if you see 2 aces go out of an 8-deck hand, there are still 30 more potential aces in the deck. The more decks you see in a game, the worse your edge against the house.
With a one deck shoe and playing perfect strategy, the house advantage in blackjack is actually +0.02 in the favor of the player. That means that if you follow basic blackjack strategy and make the right move every time, you should expect to win more money than you lose over time.
House Edge with Two or More Decks
As soon as a casino throws more decks in the shoe, the odds change drastically. Move from a single deck to a double deck shoe and you can expect your return to drop from 100.02% to 99.69%.
Here’s a breakdown of the payoffs you can expect with differently-sized shoes. Remember that this percentage assumes you’re playing perfect blackjack strategy.
1 – 100.02%
2 – 99.69%
3 – 99.57%
4 – 99.52%
5 – 99.48%
6 – 99.46%
7 – 99.45%
8 – 99.43%
The odds start to flatten out at a point, which explains why more casinos don't choose to invest in more decks for their blackjack games. The inclusion of even one extra deck has the largest impact on the outcome of the game, because an additional four cards of each rank throws off a lot of calculations. That’s why casinos use multiple decks—to stave off card counters who aren’t otherwise breaking the law.
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