Question of the Day - 11 November 2020

[Editor's Note: This question stems from the QoD of about a month ago on how many decks to practice blackjack with, written by Arnold Snyder. Mr. Snyder graciously answers this one as well.]

There are slight differences in blackjack basic strategy between single-deck and multiple-deck games. If you learn the multiple-deck basic strategy and always use it, even when you play in single-deck games, the cost in dollars and cents is negligible.

Most professional players learn one basic strategy and use it for all games. So I won't try and convince you to always use the “correct” basic strategy for the number of decks in play. But I will list the differences.

With a soft 18 (A7) versus a dealer ace, you always hit in multiple-deck games. But in single-deck, you hit if the dealer hits soft 17, but you stand if the dealer stands on soft 17.

With a total of 11 versus a dealer ace, you double down in single-deck, but hit in multiple -deck.

With A8 versus 6, you double down in single-deck, but stand in multiple-deck.

With A7 versus Ace, you stand in single-deck, but hit in multiple-deck.

With A6 versus 2, you double down in single-deck, but hit in multiple-deck.

With A2 or A3 versus 4, you double down in single-deck, but hit in multiple-deck.

With a pair of 66 versus 7, you split in single-deck, but hit in multiple-deck.

With a pair of 77 versus 8, you split in single-deck, but hit in multiple-deck.

With a pair of 77 versus Ten, you stand in single-deck, but hit in multiple-deck.

With a pair of 44 versus 4, you split in single-deck, but hit in multiple-deck.

With a pair of 33 versus 8, you split in single-deck, but hit in multiple-deck.

If surrender is allowed:

In multiple-deck, you surrender 16 (excluding 88) versus 9, Ten, or Ace. But in single-deck, you surrender 16 versus Ten, or Ace only.
In single-deck, you surrender 77 versus Ten, but in multiple-deck, you hit.

Note that there are other minor differences that depend on whether the dealer hits or stands on soft 17, whether you’re allowed to double down after splits or not, and exactly which cards make up your hand, i.e., composition-dependent basic strategy, or if the European no-hole-card rule is in effect. I hate to tell you this, but some of those multiple-deck strategies apply in two-deck games, but others do not. I’m not going to point out which ones, because this list is already too complicated. These are all borderline decisions, close to being coin flips. The best way to deal with these differences is to learn the basic strategy for the game you play most frequently and don’t worry about the differences when you play a different game. The cost is negligible. The most important differences to pay attention to are the changes you make when the dealer hits of stands on soft 17, and the pair split differences when you’re allowed to double down after splits.

Regarding the logic of these decisions, here’s one that’s easy to understand: 77 vs Ten. You stand in single-deck but hit in multiple-deck. Why? When you have a total of 14 versus a dealer Ten up, the card you would most like to get when you hit is a 7, because that would make your hand total 21 and you’re trying to beat the dealer’s possible total of 20. But since you have two 7s in your hand, in a single-deck game, 50% of the 7s are already removed from the deck. Also, because you’re holding two 7s, you’ve reduced the dealer’s odds of making a pat 17 by turning up a 7 in the hole. So, you’re slightly better off just standing and hoping the dealer busts than taking a chance with a hit.

But in a six-deck game, removing two 7s from the 24 in the shoe doesn’t have the same effect on the odds. You still have a lost of possible 7s to make your 77 pair into a 21 and the dealer still has a lot more possible 7s in the hole to give him a pat 17. So, you’re better off taking the hit. All of the above differences are based on the fact that the cards removed from a single-deck to make your hand and the dealer’s upcard have a much bigger effect than removing those three cards from a shoe. Most of these differences weren’t discovered until high-speed computers were used to analyze the hands because they’re based on the complicated possibilities of how the remaining cards might affect the final totals of both your hand and the dealer’s.

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