Single-Deck Blackjack

6 June 2021

By John Grochowski

Single-deck blackjack seems almost like a relic from the deep past. It's rare in most of the country, not common even in Nevada, and finding a single-deck game with favorable rules seems an impossible dream.

So when someone who called himself "Not Blackjack Bob" emailed me about a single-deck game he found online, I had to do double and triple takes.

He wanted to know about basic strategy and doubling down on hard 8, something that's not done with two decks or more. The game Not Blackjack Bob said he found was one deck, dealer hits soft 17, blackjacks pay 3-2, players may double down on any first two cards but may not double after splits, and players may split pairs only once.

The house edge against basic strategy players is 0.17 percent. Assuming a fresh shuffle for every hand, as is common online, card counting for purpose of sizing bets is off the menu, but the house edge is lower than is common in modern casinos.

That brings us to the question.

"I looked at basic strategy charts online," Blackjack Bob wrote. "They say to double down on hard 8 against 5 or 6. You hit those in the six-deck games I usually play.

"Why is it different with one deck? The cards are all there in the same proportions no matter how many decks."

I told Not Blackjack Bob the cards are in the same proportions immediately after a shuffle, but once cards are played the composition of the remaining cards changes more dramatically with one deck than with more.

When you double on hard 8, you make a second bet equal to your first and draw one more card. An Ace for 19 or a 10-value for 18 give you a shot to win even if the dealer makes a standing hand, and a 9 gives you a chance to push if the dealer stands with hard 17.
Starting with hard 8 removes two cards from the deck -- 4-4, 5-3 or 6-2. Having the dealer show a 5 or 6 removes a third. In a single 52-card deck, that leaves four 9s, 16 10 values and four Aces among the other 49 cards. That's 24 of 50, or 48.98 percent, that could give you a push or better if the dealer doesn't bust.

If there are six decks, or 312 cards, your starting cards plus the dealer's up card are a much smaller part of the full deck. After dealing three cards, there are 309 remaining. 24 are 9s, 96 are 10 values and 24 are aces. Those 144 cards are 46.6 percent of the cards remaining, giving you a smaller chance of drawing a desired card on your double down.

For those who want to reach beyond basic to composition-dependent strategy, note a 6-2 hard 8 favors hitting against a 6, while doubling is favored on other hands in a "no double after split" game.

By the numbers:

• 4-4: Against a dealer 6, average profits per dollar of your original wager are 18.6 cents when doubling, 16.5 when hitting and 12.6 when splitting. Vs. 5, it's double, 16.2, hit, 15.3, and split, 9.8.


• 5-3: Against a dealer 6, average profits per dollar of your original wager are 17.8 cents when doubling, 15.2 when hitting. Vs. 5, it's double, 15.5, hit, 14.0.


• 6-2: Against a dealer 6, average profits per dollar of your original wager are 11.1 cents when doubling, less than the 12.0 when hitting. Vs. 5, it's double, 13.00, hit, 12.99.

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