Ask a player what changes in single deck blackjack and the answers are usually vague: "a few doubles," "you split more." The vague answer is not wrong, but the question has an exact answer, because a basic strategy chart is a finite object and two charts can be compared cell by cell.
That is what this article does. It takes the charts the 21 Trainer app uses, one for a single deck game and one for the four to eight deck shoe game, and compares them cell by cell. Both assume the dealer peeks for blackjack, blackjack pays 3:2, doubling on any two cards, and late surrender where a cell calls for it.
The result is a complete list of exceptions to the chart you already know. Nothing else on the single deck chart moves.
What was compared
A full chart has 28 rows, hard 8 through 17, soft 13 through 20, and the ten pairs from 2,2 through A,A, each against 10 possible dealer upcards: 280 cells. Many cells carry an "if allowed" clause tied to doubling, double after split or surrender, with a fallback play. A cell counts as changed when any part of it differs, the fallback included. Two comparisons follow: the first holds the soft 17 rule fixed at dealer stands, isolating deck count; the second switches both charts to dealer hits soft 17, and the two lists turn out not to be the same list.
The 20 cells when the dealer stands on soft 17
With the dealer standing on soft 17, the single deck chart differs from the four to eight deck chart in 20 cells. The table has 18 rows, and two of them (hard 8 against a 5 or 6, and 4,4 against a 5 or 6) cover two cells each: 16 + 2 + 2 = 20. That is 20 of 280 cells, about 7 percent of the chart.
| Hand | Dealer upcard | 4 to 8 decks | Single deck |
|---|---|---|---|
| Hard 8 | 5 or 6 | Hit | Double if allowed, otherwise hit |
| Hard 9 | 2 | Hit | Double if allowed, otherwise hit |
| Hard 11 | Ace | Hit | Double if allowed, otherwise hit |
| Hard 15 | 10 | Surrender if allowed, otherwise hit | Hit |
| Hard 16 | 9 | Surrender if allowed, otherwise hit | Hit |
| Soft 13 | 4 | Hit | Double if allowed, otherwise hit |
| Soft 14 | 4 | Hit | Double if allowed, otherwise hit |
| Soft 17 | 2 | Hit | Double if allowed, otherwise hit |
| Soft 18 | Ace | Hit | Stand |
| Soft 19 | 6 | Stand | Double if allowed, otherwise stand |
| 2,2 | 3 | Split with double after split, otherwise hit | Split |
| 3,3 | 8 | Hit | Split with double after split, otherwise hit |
| 4,4 | 4 | Hit | Split with double after split, otherwise hit |
| 4,4 | 5 or 6 | Split with double after split, otherwise hit | Split with double after split, otherwise double |
| 6,6 | 2 | Split with double after split, otherwise hit | Split |
| 6,6 | 7 | Hit | Split with double after split, otherwise hit |
| 7,7 | 8 | Hit | Split with double after split, otherwise hit |
| 7,7 | 10 | Hit | Surrender if allowed, otherwise stand |
Three patterns stand out. Single deck doubles more: hard 8, hard 9, hard 11, soft 13, soft 14, soft 17 and soft 19 pick up doubles the shoe chart does not take. It splits more when double after split is allowed: 3,3, 4,4, 6,6 and 7,7 gain split plays, and 2,2 against a 3 and 6,6 against a 2 become unconditional splits. And it trades surrenders: hard 15 against a 10 and hard 16 against a 9 become plain hits, while 7,7 against a 10 becomes a surrender when the rule is offered (a stand when it is not).
These are borderline calls. Double after split already decides four of these pair cells in the shoe game, and the pair of 7s, the subject of our piece on splitting 7s, gains two single deck plays: a conditional split against an 8 and a surrender against a 10.
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Dealer hits soft 17: 21 cells, three out and four in
Switch both charts to dealer hits soft 17 and the single deck list has 21 cells. Seventeen carry over from the table above, three drop off because the two charts now agree on them (hard 11 against an ace, soft 18 against an ace and soft 19 against a 6), and four appear: soft 18 against a 2 goes from double if allowed, otherwise stand, to a plain stand; 7,7 against an ace from hit to surrender if allowed, otherwise hit; 8,8 against an ace from surrender if allowed, otherwise split, to a plain split; and 9,9 against an ace from stand to split with double after split, otherwise stand.
That is 17 plus 4, or 21 of 280 cells, 7.5 percent. Note the 8,8 change: here it is the shoe game that wants to surrender eights against an ace, and single deck refuses, playing a plain split.
The soft 17 rule inside single deck itself
One more comparison from the same chart file is smaller and stranger. Holding deck count fixed at one, the soft 17 rule moves five cells, all against an ace: hard 15 from hit to surrender if allowed, otherwise hit; hard 17 from stand to surrender if allowed, otherwise stand; soft 18 from stand to hit; 7,7 from hit to surrender if allowed, otherwise hit; and 9,9 from stand to split with double after split, otherwise stand.
One deck versus two decks
How much of this list shows up already at two decks? Our article on the double deck game lists the two deck differences against the shoe game with the dealer standing on soft 17; there are six: hard 9 against a 2, hard 11 against an ace, hard 16 against a 9, 6,6 against a 2, 6,6 against a 7 and 7,7 against an 8. All six are on the single deck list above.
So two decks make 6 of the 20 changes, and the final step down to one deck makes the other 14. The changes do not arrive evenly: most of the new doubles and the entire 4,4 group only appear at a single deck, consistent with the way the value of dropping decks is concentrated in that last step, as our comparison of single deck versus eight decks lays out.
Why fewer decks move these cells
The mechanism is concentration: every card dealt changes the composition of what remains, and the fewer cards remain, the larger each removal looms. An ace off the top weighs more in 51 cards than in 415. Our piece on the effect of removal measures that pull rank by rank for a six deck shoe, and in a single deck a two card hand is already a statement about the deck.
What concentration does not give you is a story for each cell: which borderline calls flip is an outcome of computation across the whole chart, not a chain of reasons you can reconstruct at the table. The general patterns, more doubles, more splits with double after split, fewer surrenders, are a safer thing to carry in your head than an invented justification for any one cell.
Practicing the single deck chart
Knowing the list is not the same as playing it. An exception you cannot recall in two seconds does not exist in practice, so the list belongs in drills. In 21 Trainer the charts redraw automatically for the selected rules: set the deck count to one and the soft 17 rule you want, and practice hands get instant feedback against the chart for those rules, with an explanation on every decision.
Two cautions. The app's Single Deck preset is one deck, dealer hits soft 17, no double after split and a 6:5 payout. With double after split off, every "split with double after split, otherwise" cell on these lists falls back to its second half: 3,3 against an 8, 4,4 against a 4, 6,6 against a 7 and 7,7 against an 8 hit, 4,4 against a 5 or 6 doubles, and 9,9 against an ace stands. And the 6:5 payout is the larger issue: per the figures in our piece on 3:2 versus 6:5, it raises the house edge by roughly 1.4 percentage points, close to three times the roughly half a point that single deck gives back. For the rest of the ledger, our overview of what changes with the rules covers which rules move which hands.
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Frequently asked questions
How different is the single deck blackjack chart from the shoe chart?
With the dealer standing on soft 17, 20 of the chart's 280 cells change, about 7 percent. With the dealer hitting soft 17 the count is 21, or 7.5 percent. The rest of the chart is identical. Most of the changes are extra doubles and extra pair splits, plus a few surrender calls.
Do you double down more in single deck blackjack?
Yes. With the dealer standing on soft 17, eight of the 20 changed cells are new doubles: hard 8 against a 5 or 6, hard 9 against a 2, hard 11 against an ace, soft 13 and soft 14 against a 4, soft 17 against a 2, and soft 19 against a 6. Each card already dealt weighs more in a 52 card pack, and close calls like these are where it shows.
Do you surrender 7,7 against a 10 in single deck?
Yes, when late surrender is offered. Under either soft 17 rule, the single deck chart plays 7,7 against a 10 as surrender if allowed, otherwise stand, where the shoe chart hits. With the dealer standing on soft 17 it is the one surrender single deck adds, while two shoe surrenders, hard 15 against a 10 and hard 16 against a 9, become plain hits.
Does the soft 17 rule change the single deck chart?
Yes. Going from dealer stands to dealer hits soft 17 moves five single deck cells, all against an ace: hard 15 becomes surrender if allowed, otherwise hit; hard 17 becomes surrender if allowed, otherwise stand; soft 18 goes from stand to hit; 7,7 becomes surrender if allowed, otherwise hit; and 9,9 becomes split with double after split, otherwise stand. Every other cell is unchanged.
How do you practice the single deck chart?
21 Trainer's charts redraw for the selected rules, so set the deck count to one and the soft 17 rule you want, and practice hands get instant feedback with an explanation for every decision. The Single Deck preset is one deck, dealer hits soft 17, no double after split, 6:5 payout. Free on iPhone and Android.