Knowing when to double down is an important part of blackjack basic strategy because it allows you to make more money on the good hands and make up for some of your bad hands. Doubling at the wrong time or not doubling when you should, though, will cost you money in the long run. That is why I’m writing a comprehensive guide for doubling down strategy. This part of the series covers what to do when you have a soft 15 (ace, four).
If you have a soft 15, whether or not you double depends on what up cards the dealer is showing. If the dealer shows a four, five or six, you should double down. If the dealer shows anything else, you should hit. You should never stand with a soft 15 because 15 is a bad hand and you have no risk of busting.
Blackjack basic strategy takes into account that there are more cards with a value of 10 (4/13) than any other value (1/13 each). Therefore, the odds are that the dealer’s hole card is a 10 and any cards drawn will have a value of 10. Obviously, this doesn’t always happen, since there are 9/13 odds against it, but in the long run taking advantage of the high number of tens is good strategy.
For that reason, if the dealer shows a four, five or six, you should assume the high probability of the dealer having a hand of 14, 15 or 16. Those are all stiff hands (12-16), which are very bad because of the high probability of busting. The dealer does not have the option of standing on a stiff hand, though, so he must take a hit. If the dealer busts, you win no matter what cards you have (as long as you don’t also bust). For that reason, doubling your bet when the odds are with the dealer busting makes sense. Let’s look at each of the hands.
If the dealer has a hard 14, there are only five cards (3, 4, 5, 6, 7) that will improve his hand, six cards (8, 9, 10, J, Q, K) that will cause him to bust, and two cards (ace, 2) that will leave him with another stiff hand. If the dealer has a hand of 15, only five cards (2, 3, 4, 5, 6) will improve his hand, while seven cards (7, 8, 9, 10, J, Q, K) will cause him to bust. If the dealer draws an ace, that gives him a hand of 16, which is another stiff hand. If the dealer has a hand of 16, only five cards (ace, 2, 3, 4, 5) will improve his hand, while eight cards (6, 7, 8, 9, 10, J, Q, K) will cause him to bust. Looking at it that way, if the dealer has a hand of 14, 15 or 16 he has 8/13 odds against him.
If the dealer has a hard 12 or 13, he still has a stiff hand, but is less likely to bust than with a 14-16. If the dealer doesn’t bust, you need to beat his hand. If you double down, you only get one more card. If you have a soft 15 and double, there are eight cards (ace, 7, 8, 9, 10, J, Q, K) that would leave you with a total below 16. There are five cards (2, 3, 4, 5, 6) that would give you a hand of 17 or greater. However, two of those cards (2, 3) would leave you with a soft hand that you would normally hit against a dealer 14-16. If you double, though, you cannot hit again.
Therefore, doubling a soft 15 results in 7/13 odds that, if the dealer doesn’t bust, you would wish you could hit again. For that reason, you only want to double your wager if the dealer has 8/13 odds against him, as is the case with a hand of 14-16.