Card counting is a card game strategy used to determine when a player has a probability advantage. The term is used almost exclusively to refer to the tracking of the ratio of high cards to low cards in blackjack, although theoretically card counting can be used in some other card games.
How card counting works in blackjack
Card counting is based on the fact that high cards, and especially aces, are good for the player while low cards are good for the dealer. High cards are good for the player because they increase the chance of a player getting a “blackjack”, which usually pays 3 to 2. High cards also increase the player’s chance of success on his pair splits and double downs. Low cards are good for the dealer because they decrease the chance that the dealer will bust.
Card counters raise their bets when the ratio of high cards to low cards in the deck is skewed in their favor. They also make strategy adjustments based on the ratio of high cards to low cards. These two adjustments to their betting and playing strategy can give players a small mathematical advantage over the house.
Contrary to the popular myth, card counters do not need savant qualities in order to count cards, because they are not tracking and memorizing specific cards. Instead, card counters assign a heuristic point score to each card they see and then track only the total score. (This score is called the “count”.)
Different card counting systems assign different point values to various cards, but one of the most common systems, the Hi-Lo Count, is illustrative. In this system, the cards numbered 2 through 6 are counted as +1 and all tens (which include 10s, jacks, queens and kings) and aces are counted as -1. The cards 7, 8, and 9 are given a count of 0. The Hi-Lo system exemplifies a “level one” counting system; other counting systems also assign +2 and -2 counts to certain cards and are called “level two” systems. Many card counting experts agree that the additional accuracy derived from a “level two” system is offset by the increased difficulty of keeping count and the greater likelihood of making a mistake.
Another commonly used card counting system is the “K-O”, an unbalanced card counting system derived from Arnold Snyder’s unbalanced Red 7 count, published in 1981. The first blackjack researcher to publish an unbalanced card counting system was Jacques Noir, in his 1968 book Casino Holiday. Unbalanced card counting systems eliminate the need to estimate remaining decks to be dealt, a common source of player error in card counting.