Card counting is a perfectly legal but, understandably, heavily discouraged, strategy employed by players of blackjack and similar games to reverse the inherent house edge in their favour. As the name suggests, card counting involves keeping a running tally of all the cards dealt to the player doing the counting, the other players and the dealer. Card counting is based on the presupposition that a deck of cards rich in aces, court cards and/or tens is favourable to the player, while a deck rich in low value cards is favourable to the dealer, and vice versa.
The simplest form of card counting, known as ‘Hi-Lo’, assigns each card that passes a value of -1, 0 or +1, depending on how favourable it is to the player. Aces, court cards are assigned a value of -1, sevens, eights and nines are assigned a value of 0 and any card lower than a seven is assigned a value of +1. The player keeps a ‘running’ count, by adding or subtracting the appropriate value for each card. When the count is positive, the odds are in favour of the player, who can increase his/her stake, and adjust his/her playing strategy, accordingly.
The running count, alone, is only effective in single-deck blackjack so, to dissuade card counters and increase the house edge, many casinos operate six-deck blackjack games, as standard, and even up to eight-deck games. Multiple decks add an extra level of complexity to card counting, but the problem can be solved by estimating the number of decks remaining and dividing the running count by that number to give the so-called ‘true’ count.