Does It Help or Hurt when Blackjack Dealers Hit Soft 17s?

Puzzling out the answer intuitively doesn't necessarily work. Basic Strategy tells bettors with soft 17 to hit or double, suggesting that a dealer doing likewise would favor the house. On the other hand, think about players sitting on 16s or below against six, figuring the dealer for a bust, then losing when the hole card turns out to be an ace for a total of 17. What if the dealer had to draw? Solid citizens with stiffs don't lose any worse if a 17 is improved, and there seems to be a good chance that the dealer, drawing, will bust and pay everyone. Doesn't this imply that the dealer hitting soft 17 favors the players?

The proof is in the probabilities. Calculations for the options show that the casino has a greater edge when dealers hit rather than stand on soft 17s. For eight-deck games with no resplitting, assuming players can double on any two-card hands including those formed by splits, overall house advantage for perfect Basic Strategy is 0.486 percent if dealers stand on soft 17s, and 0.699 percent if they hit. Games in which dealers hit soft 17 therefore have nearly half again as much house advantage as those in which they stand on this total. The penalty is sizeable.

The accompanying table shows how the phenomenon evolves. Entries give expectations under the cited playing conditions for each dealer upcard, as well as the difference between the two cases. Positive differences indicate worse and negative values better prospects for bettors in the dealer switching from stand to hit.

Expectations for games in which dealers must stand on or hit soft 17, assuming eight decks, double after splitting, double on any two cards, no resplitting.

Expectations for alternate dealer action on soft 17
(Percent of initial wager won/lost)

The data confirm intuition about rounds when dealer have six-up. Players do better in this case when the dealer must hit soft 17. They're favored significantly either way with over 23 percent edge, six still being the weakest dealer upcard. But players' expectations are slightly greater (by 0.292 percent) under the "hit" rule. Players also get a happier shot against fours and fives. Here again, the data show they're firmly in the driver's seat either way, although marginally more strongly -- 0.041 percent and 0.022 percent, respectively -- when the dealer hits.

On dealers' twos and threes, players also have a decent edge. However, it's fractionally less when the dealer must hit soft 17. The respective differences are 0.026 percent and 0.021 percent. Edge is the same with either rule when the dealer starts with seven through 10 because these upcards can't lead to soft 17.

The big factor is ace-up. Of course, dealers are strong with this card, but much more so -- the premium being 3.084 percent -- when they hit soft 17s. The reason hitting soft 17 boosts the house edge so much with a dealer's ace has its roots in two key points about blackjack. First, 17 is a weak hand; it pushes another 17 and loses to any other "made" total. Second, when the dealer holds an ace, no Basic Strategy player will be sitting on a stiff; everyone will have hit totals of 16 or below, and will either have busted or be waiting with a total of 17 through 21.

So a dealer hitting can only hurt the house, and might help it, against players with 17. And it can only abet the bosses against bettors counting their money with totals of 18 through 21. As the beloved bard, Sumner A Ingmark, rhymingly remarked:

A rule experience should have taught,
Is overconfidence comes to naught.