Blackjack card counting is a blackjack strategy that's 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 a blackjack game (and related games such as Spanish 21).
The logic behind blackjack card counting is that a deck of cards with a high proportion of high cards (ten-valued cards and aces) to low cards is good for the player, while the reverse (a deck with a high proportion of low cards to high cards) is good for the dealer. In theory, a deck that is rich in tens and aces improves the player's odds because blackjacks (which offer a higher payout than other winning hands) are more likely to happen, the dealer is more likely to bust, and double-downs are usually more successful.
Basic blackjack card counting assigns a positive, negative, or null value to each card that is dealt. As each card is dealt, the running count is adjusted by each card's assigned value. There are several card-counting systems in use these days. Below we look at a couple.
The Hi-Lo System - In the Hi-Lo system, the cards 2 through 6 are assigned a value of +1. Tens (and face cards) through aces are assigned a value of -1. Cards 7, 8, and 9 have a value of zero, or are called neutral (so they can be ignored). The Hi-Lo system is a perfect example of a balanced card-counting system. By this we mean that there are an equal number of +1 and -1 cards in the deck, so a count of all 52 cards would result in an end count of 0. The Hi-Lo system is considered a single-level or level-one count system, because the count never increases or decreases by more than one.
Other Blackjack Card Counting Systems - Zen Count or Wong Halves are two systems which are said to use a multilevel count. These systems make finer distinctions between card values to gain greater play accuracy. Rather than all cards having a value of +1, 0, or −1, an advanced count might also include card ranks that are counted as +2 or −2. Advanced players might additionally maintain a side count of specific cards, such as a side count of aces, to deal with situations where the best count for betting accuracy differs from the best count for playing accuracy.
We'll be adding more about blackjack card counting soon, so stay tuned.