Basic strategy covers those situations in which it is advisable to double down and those in which doubling down is inadvisable, however it is important to understand the reasons that determine the optimum choice as there are always times when one is tempted to stray from basic strategy to play a hunch at a casino table. We always advise you not to play hunches, but we can’t stop you doing so, thus the best we can do is to try to explain the reasons behind choosing when to and when not to double down.
Doubling down, just as all actions defined in basics strategy, is a way of reducing the house edge.
First let’s look at the probability of a dealer busting given that they are showing a specific card. These are the figures (the first number is the up car and the second the percentage of times that hand will bust):2-35%; 3-37%; 4-40%; 5-42%; 6-42%; 7-26%; 8-24%; 9-23%; 10-23%; Ace-17%.
As you can see, there is a huge difference between the dealer’s probabilities of busting when she shows a 5 compared to when she shows a 7 to an Ace. The time to double down is when the dealer has a greater chance of busting and you have a strong hand.
The kinds of hands that you should consider doubling down are when your hard count is 9, 10 or 11 and when you have an Ace matched with a 2 to a 7. If you look at a basic strategy chart and read it in terms of the above data, it will become clear why you are advised to double down in specific circumstances.
Our advice is to never divert from basic strategy and never play your hunches, but if you find that you prefer to ignore this advice, then remember that you must never double down if there is any chance that you can bust on a single card games.