The basic strategy of card counting provides the player with the optimal play for any blackjack situation in the long run. By keeping track of the cards that have already been played, it is possible to know when the cards remaining in the deck are advantageous for the player.
Card counting creates two opportunities:
- The player can make larger bets when he has the advantage. For example, the player can increase the starting bet if there are many aces and tens left in the deck, in the hope of hitting a blackjack.
- The player can use information about the remaining cards to improve upon the basic strategy rules for specific hands played. For example, with many tens left in the deck, the player may double down in more situations since there is a better chance of making a strong hand.
Virtually all card-counting systems do not require the player to remember which cards have been played. Rather, a point system is established for the cards, and the player keeps track of a simple point count as the cards are played out from the dealer.
Depending on the particular blackjack rules in a given casino, basic strategy reduces the house advantage to less than 1%. Card-counting, if done correctly, can give the player an advantage, typically ranging from 0 to 2% over the house.
Card-counting mentally is legal and is not considered cheating. However, most casinos have the right to ban players, with or without cause, and card-counting is frequently used as a justification to ban a player. Usually, the casino will inform the player that he is no longer welcome to play blackjack at that casino and may be banned from the property. Players must be careful not to signal the fact that they are counting, and the use of electronic or other counting devices is usually illegal.
Basic strategy is based on a player’s point total and the dealer’s visible card. A player’s ideal decision may depend on the composition of his hand, not just the information considered in the basic strategy. For example, a player should ordinarily stand when holding 12 against a dealer 4. However, in a single deck game, the player should hit if his 12 consists of a 10 and a 2; this is because the player wants to receive any card other than a 10 if hitting, and the 10 in the player’s hand is one less card available to cause a bust for the player or the dealer.
However, in situations where basic and composition-dependent strategy lead to different actions, the difference in expected value between the two decisions will be small. Additionally, as the number of decks used in a blackjack game rises, both the number of situations where composition determines the correct strategy and the house edge improvement from using a composition-dependent strategy will fall. Using a composition-dependent strategy only reduces house edge by 0.0031% in a six-deck game, less than one tenth the improvement in a single-deck game (0.0387%).