Card counting allows the player to turn the house advantage into an maximum player advantage of approximately 1%. The basic principle behind card counting is that a deck rich in high cards (tens and aces) benefits the player, while a deck rich in small cards benefits the dealer.
The card counter assigns a value to each card that is dealt out of the shoe and maintains a running count. A negative value is assigned to high cards, a positive value to small cards, and a neutral value to medium cards, depending on the counting system. When the count is high, indicating a deck that is rich in high cards, the card counter steps up his betting aggressively. When the count is negative, the card counter bets small, or leaves the table altogether.
Hi/Lo is a simple, popular and relatively effective counting system. The card count values for each card dealt is shown in the chart to the right. Start at 0, and for each card dealt from the shoe, add or subtract 1 from the count depending on the card. You should learn to ignore the 0 value cards. This count is called the
running count. Divide the running count by the number of decks remaining in the shoe (you'll have to determine this through practice) to determine the
true count. When the true count is +2 or above, the deck is rich in high cards, and thus the odds are favorable to the player.
Card counting is not only difficult to master, but the casinos don't like it. As told in books like
Bringing Down the House and TV shows like
Breaking Vegas, professional card counters have been banned, harassed and investigated by the casinos they profit from. Although card counting is not technically illegal, casinos are private entities who can ban anyone they want from the premises.
Savvy card counters must engage in elaborate ruses to avoid arousing suspicion from the pit bosses (e.g. a tourist from Duluth "just visiting" for the weekend). If the casino suspects a player of card counting, more than likely the pit boss will politely ask the player to play any game other than blackjack. In the worst case scenario, they can ban the player from the casino permanently and place their photo in a widely-used database of known card counters.
It is possible to win at blackjack with card counting, but it's risky and requires discipline, practice and determination. Only experienced players who know what they are doing should attempt card counting in a casino.