Blackjack Playing Strategies

Basic Blackjack Playing Strategies 
The following is a summary of the correct double down basic strategy for multiple decks and doubling after pair splitting. (The use of single decks and exclusion of doubling after splitting will change certain decisions).  
If your two card hand totals hard 11 (e.g. 7,4), double down if the dealer's upcard is 2 through 10 (hit if the dealer's upcard is an ace).   
If your two card hand totals hard 10 (e.g. 6,4), double down if the dealer's upcard is 2 through 9 (hit if the dealer's upcard is a ten or ace).  
If your two card hand totals hard 9 (e.g. 6,3), double down if the dealer's upcard is 3 through 6 (hit if the dealer's upcard is any other value).   
If your two card hand totals soft 17 or 18 (e.g. A,6 or A,7), double down if the dealer's upcard is 3, 4, 5 or 6).   
If your two card hand totals soft 15 or 16 (e.g. A,4 or A,5), double down if the dealer's upcard is 4, 5 or 6.   
If your two card hand totals soft 13 or 14 (e.g. A,2 or A,3), double down if the dealer's upcard is 5 or 6.  
The use of a single deck affords the player more opportunities to double down. This includes doubling 11 vs. dealer ace doubling 9 vs. dealer 2 doubling 8 vs. dealer 5,6 doubling A,8 vs. dealer 6 doubling A,6 vs. dealer 2 doubling A,2 and A,3 vs. dealer 4. 
 Also, if doubling down after pair splitting is not allowed, you should also double down on 4,4 vs. a dealer's 5 and 6.  
he complete double down strategies are presented in the tables in Appendix I.  
Let's take a moment and explain the reasons for these double down strategies. 
 Your two card hands that total 9, 10 or 11 should be doubled because you have an excellent chance of obtaining a pat hand by drawing a ten value card. As discussed in the previous section, soft doubling is recommended when the dealer has a high probability of busting (dealer has a low value upcard). Remember, that you can only double down on your first two cards. Once you draw a third card to any particular hand, the double down option is no longer available.
  In an earlier section, a computer method used to determine the "best" playing strategy was discussed. It depended on comparing the percentage of hands won or lost on standing or hitting a particular hand versus dealer's upcard. Doubling down must be evaluated in a different manner and for the benefit of the readers who wish to know how this is accomplished mathematically, an example is provided. 
 To evaluate if doubling down is the better strategy versus hitting, the amount of money wagered per hand must be considered. For example, computer analysis shows that:  
If you hit a hand of 11 versus a dealer's 8, then you can expect to win 61 % of the hands and lose 39%. Assuming you wager $1 per hand, the net dollar won per hand would be: (61%-39%) x $1 = 22 cents per hand. 
 If on the other hand you double down on 11 versus an 8, you can expect to win 59% of the hands and lose 41 %. Note that you will win less hands doubling than by hitting. This is because if you receive a low value card by hitting you have an opportunity to improve the hand by further drawing. If you double you receive only one card and cannot draw additional cards. Assuming you wager $1 per hand, the net dollar won per hand by doubling down would be: (59%-41%) x $2 (extra double down bet) = 36 cents per hand. Clearly doubling gains you fourteen cents per hand (36- 22) as opposed to hitting. 
 
Similar calculations are used to determine the soft doubling rules.  

Pair Splitting 
 In general, a hand should be split vs. an alternate playing strategy such as standing or hitting if it meets one of the following criteria: 8.You will win more, on average or 9.You will lose less, on average or 10.You turn a losing hand into a winning hand.