In blackjack the dealer takes two cards and shows you one of them. That exposed card is the upcard; the other, face down, is the hole card. Basic strategy is a table with your hand down one side and the dealer's upcard along the top, and the upcard axis is the one doing most of the work: the same hard 16 is a stand against a 6 and a hit against a 7.
A dealer showing a 6 busts 42.32% of the time. A dealer showing an ace busts 16.65% of the time. Both figures are under the stand-on-soft-17 rule and come from playing the dealer's hand out over every possible draw.
The cliff sits between 6 and 7. From a 2 through a 6 the dealer must draw to a stiff total that any ten-valued card breaks, and four of the thirteen ranks are worth ten. From a 7 upward a single ten makes a safe 17 and the dealer stops: the bust chance drops from 42.32% on a 6 to 26.23% on a 7, more than a third gone in one rank. That gap is why the chart tells you to stand on totals that cannot win on their own against a small upcard, and to keep hitting them against a large one. You are not betting on your cards; you are betting on the dealer's.
Two table procedures hang off the upcard as well. When it is an ace the dealer offers insurance, a side bet on the hole card being a ten that costs 6.80% on a six-deck shoe. When it is a ten or an ace, most American tables have the dealer peek at the hole card before anyone acts, so a dealer natural ends the hand before you can double or split into it.
Whether the dealer hits or stands on soft 17 shifts the whole column by a fraction of a point rather than reordering it; the H17 column on the computed page shows the ace rising from 16.65% to 20.07% and the small cards barely moving.
Where the numbers come from
- Dealer bust chance for every upcard, S17 and H17
- The full decision table those figures produce
- Insurance, costed
Related terms in casino floor
- Soft 17, A hand of 17 counting an ace as eleven. Whether the dealer stands or hits on it is printed on the table, and it is worth 0.22 percentage points.
- Insurance, The side bet offered when the dealer shows an ace. Every source calls it a bad bet; this one gives the figure, and it changes with the number of decks.
- Natural, A hand that wins immediately on the first cards dealt.
- Surrender, Folding a bad hand for half your stake. It is the one rule that moves the edge the player's way, and most tables do not offer it.
Where an entry quotes a number, that figure comes from the computed sections of this site rather than from another glossary, so the definition and the derivation cannot drift apart. Each entry links to the page where the number is worked out.