Why should you always use basic strategy? Because blackjack is not a game that rely on intuition. Blackjack it's mostly based on your skill. So, a good player can change the casino's normal edge by choosing a good strategy/system of playing and in some occasion he can even gain an edge over the casino.
The basic strategy (for a particular set of rules) was developed by intensive computer simulation, which performed a complete combinatorial analysis. The computer played tens of thousands of hands for each blackjack situation possible, then statistically decided as to which play decision favored the player. The charts below are the results of this computer analysis.
Legend
H = Hit
S = Stand
D = Double
P = Split
Las Vegas Single Deck Basic Strategy Table
| Dealer's Up Card |
Your Hand | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | A |
| 8 | H | H | H | D | D | H | H | H | H | H |
| 9 | D | D | D | D | D | H | H | H | H | H |
| 10 | D | D | D | D | D | D | D | D | H | H |
| 11 | D | D | D | D | D | D | D | D | D | D |
| 12 | H | H | S | S | S | H | H | H | H | H |
| 13 | S | S | S | S | S | H | H | H | H | H |
| 14 | S | S | S | S | S | H | H | H | H | H |
| 15 | S | S | S | S | S | H | H | H | H | H |
| 16 | S | S | S | S | S | H | H | H | H | H |
| 17 | S | S | S | S | S | S | S | S | S | S |
| A,2 | H | H | D | D | D | H | H | H | H | H |
| A,3 | H | H | D | D | D | H | H | H | H | H |
| A,4 | H | H | D | D | D | H | H | H | H | H |
| A,5 | H | H | D | D | D | H | H | H | H | H |
| A,6 | D | D | D | D | D | H | H | H | H | H |
| A,7 | S | D | D | D | D | S | S | H | H | S |
| A,8 | S | S | S | S | D | S | S | S | S | S |
| A,9 | S | S | S | S | S | S | S | S | S | S |
| A,A | P | P | P | P | P | P | P | P | P | P |
| 2,2 | H | P | P | P | P | P | H | H | H | H |
| 3,3 | H | H | P | P | P | P | H | H | H | H |
| 4,4 | H | H | H | D | D | H | H | H | H | H |
| 6,6 | P | P | P | P | P | H | H | H | H | H |
| 7,7 | P | P | P | P | P | P | H | H | S | H |
| 8,8 | P | P | P | P | P | P | P | P | P | P |
| 9,9 | P | P | P | P | P | S | P | P | S | S |
| 10,10 | S | S | S | S | S | S | S | S | S | S |
Las Vegas Multiple Deck Basic Strategy
| Dealer's Up Card |
Your Hand | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | A |
| 8 | H | H | H | H | H | H | H | H | H | H |
| 9 | H | D | D | D | D | H | H | H | H | H |
| 10 | D | D | D | D | D | D | D | D | H | H |
| 11 | D | D | D | D | D | D | D | D | D | H |
| 12 | H | H | S | S | S | H | H | H | H | H |
| 13 | S | S | S | S | S | H | H | H | H | H |
| 14 | S | S | S | S | S | H | H | H | H | H |
| 15 | S | S | S | S | S | H | H | H | H | H |
| 16 | S | S | S | S | S | H | H | H | H | H |
| 17 | S | S | S | S | S | S | S | S | S | S |
| A,2 | H | H | H | D | D | H | H | H | H | H |
| A,3 | H | H | D | D | D | H | H | H | H | H |
| A,4 | H | H | D | D | D | H | H | H | H | H |
| A,5 | H | H | D | D | D | H | H | H | H | H |
| A,6 | H | D | D | D | D | H | H | H | H | H |
| A,7 | S | D | D | D | D | S | S | H | H | H |
| A,8 | S | S | S | S | S | S | S | S | S | S |
| A,9 | S | S | S | S | S | S | S | S | S | S |
| A,A | P | P | P | P | P |