Why is blackjack better for players when dealers must stand on soft 17?

How often in blackjack have you stood on a total of 16 or less against a six-up, or doubled down and finished at or below this level, thinking you’re still in decent shape because the dealer has a stiff and is probably going to bust? Then, in the most common version of the game, watch the dealer turn over an ace and stand on the soft 17, beating you then and there.

You’re most likely aware that in some casinos, the dealer hit soft 17s. And you wouldn’t be alone assuming this rule is favorable to players because dealers won’t automatically prevail with pat hands against 12s through 16s.

All other things being equal, though, you’d be wrong. The house’s edge is nearly half again as great when the dealer has to hit and not stand on soft 17s; it’s on the order of 0.7 as opposed to 0.5 percent in a typical eight-deck game. Further, to keep the penalty as small as possible when going from games in which dealer stands to hits on soft 17, you have to make two changes in Basic Strategy that don’t always appear on those wallet-sized cue cards. These are to double as opposed to hit on both soft 18 versus two-up and soft 19 versus six-up. Not that the effect is very big; the former enhances expectation by only $0.93 and the latter $0.35 per $100 bet at the start of the round. But optimum Basic Strategy is more often than not a matter of small distinctions that are cumulatively large enough to keep the bosses in their silk and cashmere suits.

It’s true, of course, that a dealer with soft 17 who has to hit may exceed 21, in which case solid citizens with 16 or less will win. And this rule does raise the chance of the dealer busting with six-up from 42.29 to 43.93 percent. But, what about the effect on blackjack buffs with 17 or more? If the dealer finishes with 17, they’d push with their own 17s and win with anything higher. The fly in the ointment is the trade-off between dealers busting and the frequency at which they improve their scores, finishing with 18 to 21, and therefore beat better player totals.

The accompanying table shows the impact on final dealer hands for eight deck games, when they hit rather than stand on soft 17. Negative numbers in the table at final 17 indicate how less apt the associated result is to be achieved when the dealer has to hit than stand. Positive amounts signal how more likely they are to occur with this requirement. The top six rows give the differences in chances of busts and totals from 17 through 21; the bottom three rows show the change in likelihood of the dealer having a result worse than 17 (by busting), equal to 17, or better than 17. Data are given only for ace- and two- through six-up because the other upcards can’t yield soft 17.

Change in probability of dealers’ final results when the blackjack rule is changed so dealers must hit rather than stand on soft 17

final result/upcard     2       3       4       5       6       ace      overall
Bust                  0.32%   0.28%   0.26%   0.12%   1.64%    3.42%     0.465%
17                   -0.96%  -0.85%  -0.81%  -0.37%  -5.06%  -10.54%    -1.430%
18                    0.16%   0.14%   0.14%   0.06%   0.84%    1.75%     0.238%
19                    0.16%   0.15%   0.14%   0.07%   0.86%    1.79%     0.244%
20                    0.17%   0.14%   0.13%   0.07%   0.86%    1.79%     0.243%
21                    0.16%   0.14%   0.14%   0.07%   0.86%    1.79%     0.243%
worse                 0.32%   0.28%   0.26%   0.12%   1.64%    3.42%      0.46%
same                 -0.96%  -0.85%  -0.81%  -0.37%  -5.06%  -10.54%     -1.43%
improve               0.65%   0.57%   0.55%   0.27%   3.42%    7.12%      0.97%

Comparing the probability differences in the rows for the dealer finishing worse and improving puts the frosting on the cake. For every upcard where a soft 17 is possible, the dealer’s final hand is strengthened more than twice as frequently as it’s weakened.

The impression held by many blackjack buffs that the casinos are granting them a concession by requiring dealers to hit soft 17s demonstrates how much more there is to proficiency in gambling than meets the eye. In blackjack particularly, Shakespeare’s Hamlet had it right when he told Horatio “There are more things in heaven and earth... than are dreamt of in your philosophy.” Not to be too far outdone, the punters’ poet, Sumner A Ingmark, penned: