Many casinos offer the option to double up on a single hit card. Some of us look to divine inspiration on when to double up, others use a lucky charm, I myself like to use mathematics.
There are some hard and fast rules about when to Double Down. They are as follows.
If you have 11 you can double. There is a 30% chance of making 21 and no way to bust out. If you do make 21 the dealer can only beat you with a Blackjack and even then you’ll have your money returned.
If you have a hand of 10 you can double. The odds of winning are similar to that of if you have 11 and you have no chance of going bust.
If you have 7/8/9 don’t double. As tempting as it is that you might make 17, 18, 19 or even 20 it is unlikely. Any card other than a 10 will leave you with a vulnerable hand. The only exception to this is if you have a nine and the dealer had a low (2-6) up card and thus has a good chance of going bust.
If you have 12 or more DON’T DOUBLE. As tempting as it may be when you see the dealer has a card that means he is likely to go bust. You also have a high chance of busting and losing out.
What you must remember with Doubling Down is that you can only have one further card.
I would stress that doubling up can also affect the effectiveness of your betting strategy. Especially if you are using the Paroli or Martingale system. You should make the decisions about when you are going to Double Down and stick to them so you don’t click the double button on a whim.