Single-Deck Basic Strategy

Those whose casino memories stretch back far enough may recall a time when the standard "Las Vegas Strip" blackjack game was dealt from a single deck of cards, with the dealer standing on all 17s.

That started to change in the 1960s as operators grew ever more fearful of card counters, and today most casino blackjack games use multiple decks.

That affects all players, not just card counters. That once-standard Strip game is just about a dead heat for basic strategy players, with a 0.001 percent edge to the player. But going from one deck to two gives the house a 0.34 percent edge, and the house edge increases with every deck added, to 0.55 percent with six decks and 0.57 percent with eight decks.

The house can give back a little of the edge with positive rules, or take even more with negative ones, but given otherwise equal rules, the house edge is lower with fewer decks.

Why? Because the effect on the composition of the remaining deck of removing cards through play is greatest when a single deck is used.

Let's say we're dealt a 5 and a 6, and the dealer's up card is an Ace. In a single-deck game, 16 of the other 49 cards in the deck are 10-value cards, giving us a 32.7 percent chance of drawing a 10 value on our next card for a 21. But in a six-deck game, where 96 of the remaining 309 cards are 10 values, our chances of drawing a 10 value are only 31.1 percent.

That makes it a more favorable play to double down on 11 vs. a dealer's Ace in a single-deck game than when multiple decks are used. And that forces a change in basic strategy: In multiple-deck games, we double down on 11 when the dealer shows anything but an Ace. In single-deck games, we double against the Ace, too.

To get the most out of the single-deck game, we make a number of little strategy changes from basic strategy for multiple-deck games:

Single-deck variations for hard totals

• Double down on 11 against all dealer up cards, instead of just doubling against 2 through 10.
• Double down on 9 against 2 through 6 instead of 3 through 6.
• Double down on 8 against 5 or 6 instead of just hitting against all up cards.

Single-deck variations for soft totals

• With Ace-8, double down against 6 instead of just standing against all up cards.
• With Ace-7, stand against a dealer's Ace if the dealer stands on all 17s. If the dealer hits soft 17, or in multiple-deck games, hit soft 18 vs. an Ace.
• With Ace-6, double down against 2 through 6, instead of just doubling against 3 through 6 as we do in multiple-deck games.
• With Ace-3 or Ace-2, double down against 4, 5 or 6 instead of just against 5 and 6, as in the multiple-deck game.

Single-deck variations for splitting pairs

• With 2-2, if doubling after splits is permitted, split against 2 through 7 regardless of the number of decks. If not, split against 3 through 7 in single-deck blackjack, but only 4 through 7 in multiple-deck.
• With 3-3, if doubling after splits is permitted, split against 2 through 8 in single-deck, 2-7 in multiple-deck. If doubling after splits is not allowed, just split against 4-7 regardless of the number of decks.
• With 4-4, never split if doubling after splits is not permitted. If it is, split against 4, 5, or 6 in single-deck blackjack, but just 5 or 6 in multiple-deck.
• With 6-6, if doubling after splits is permitted, split against 2 through 7 in single-deck blackjack, but just 2-6 with multiple decks. If you can't double after splits, split against 2 through 6 with one deck, 3 through 6 with multiple decks.
• With 7-7, if doubling after splits is permitted, split against 2 through 8 with one deck, 2 through 7 with multiple decks. Split against 2 through 7 in all games if doubling after splits is not permitted. Also, hit 7-7 against a 10 in multiple-deck games, but stand in single-deck blackjack.