Welcome to the first in what will be a long continuing series on blackjack strategy for doubling down. Knowing when to double is a big part of blackjack basic strategy and it helps reduce the house edge to as small as 0.5%. First of all, let me say that in this series I will only cover the hands with which you might double. If I don’t mention a hand, such as a hard eight, you would never double with it. The first hand that I will cover is a hand of nine.
If you have a hand of nine, you should double down if the dealer shows a 3 through 6 as an up card. If the dealer shows anything else, you should hit. You should never stand with a nine because there is no risk of busting.
In blackjack, basic strategy isn’t always about maximizing the potential of your good hand. Sometimes it’s about taking advantage of a bad dealer hand. In this case, you are doubling because the dealer has a good chance of busting. If the dealer busts, you win even if you don’t have a good hand, as long as you don’t bust as well.
If the dealer shows a three through a six, he has a good chance of having a 13-16, which are stiff hands. This is because there are more cards with a value of 10 (4/13) than any other value. That means there is a high probability that the dealer has a 10 in the hole. Stiff hands are bad for the dealer because they have a high probability of busting.
Take a 13, for example. If the dealer has a hand of 13, only five cards (4, 5, 6, 7, 8 ) can help him. Three cards (ace, 2, 3) still leave the dealer with a stiff hand, meaning the dealer would have to draw again with a good chance of busting. That leaves five cards (9, 10, J, Q, K) that will cause the dealer to bust. If you’re scoring at home, that means if the dealer has a 13, he as 5/13 odds of not busting, 5/13 odds of busting, and 3/13 odds of ending up with another stiff hand and having to draw again.
The odds only get worse for the dealer as the stiff hand gets larger. If the dealer has a hand of 16, only 5 cards (ace, 2, 3, 4, 5) can help him. That leaves eight cards (6, 7, 8, 9, J, Q, K) that would cause the dealer to bust.
Those are very good odds for the player. Therefore, it is best to play the percentages, double your bet, and hope the dealer busts. Even if the dealer doesn’t bust, which goes against the odds, you are probably to draw a 10 when you double down, which would leave you with a hand of 19. There are only two hands (20, 21) that the dealer can draw that would beat that hand. Therefore, doubling your bet is a wise decision if the dealer has a two, three, four, five or six as an upcard. If the dealer shows anything else, take a hit.