Doubling down a hand increases your bet size to double the original amount wagered. In exchange for the doubling of your bet you receive one and only one card from the dealer. There are a couple rules to live by when considering doubling down. The easiest one to remember is when you are dealt an 11. In this instance, you will always double down regardless of what the dealer is showing. Because the most populous card in the deck is a 10 you will get 21 often.
The next rule to consider is what happens pertaining to a 10. When you are dealt a 10 you will want to double down only when the dealer shows a 2 through a 9. Doubling on a 10 or ace is foolish as the odds are then in the casino’s favor.
The last card you should double on is a 9. In this instance, you should only double when the odds are in favor of the dealer going bust. In other words, you will only double down when the dealer is showing a 2 through a 6.
With no other cards should you double down. With cards over 11, this rule is fairly self-explanatory—doubling down gives you a high risk of busting while increasing the amount that you can lose. This rule even goes for when you have an 8 up against a dealer’s 6. Even if you think the dealer will bust, it is most cost effective to hit, rather than double down. Hitting ends up being a much more profitable play over the long run.