This strategy has been the subject of many books, even a movie called "21" has been made about it. So, what is it all about?
Card counting is based on a simple principle: If the stack of cards used in the game has more high cards than low cards, your advantage over the casino increases.
In such case, you can even have a positive long term advantage over the casino. The advantage of the player can often reach 2% or more. On the contrary, if the cards are mainly of low values, the edge of the casino increases. When applying the strategy, you increase your bets when you have an advantage, and vice versa, when the advantage goes back to the casino's side, you reduce your bets.
In the film mentioned above, players from one team were sitting at different tables. When the statistical advantage arose on any of the tables, another player from another table was given a secret signal to join the table and to place the highest bets. Naturally, all fun ended as soon as the team had been caught by the casino.
The basic strategy of card counting works as follows:
- The cards 2 to 6 have a value of +1
- Aces, tens and picture cards have a value of -1
- The remaining medium cards 7, 8 and 9 have a value of 0
It is thus clear that the higher the total sum is, the higher your bet should be. At the same time, the total sum is divided by a multiple of the remaining card decks. Most commonly, blackjack is played with 6 to 8 decks of cards. If there are 4 packs remaining, you should divide your total sum by 4. By doing this division you will get a so-called "true count" indicating your current advantage or disadvantage. If the number of remaining decks to deal is lower while total positive sum remains the same, your advantage is higher.
Each point of true count reduces the house edge by approximately 0.5%. The player therefore has a significant advantage when the true count is 2 or higher.
It should also be noted that the basic strategy needs to be tweaked as counts of cards in the shoe change. For example, as I previously mentioned, if your total is 15 against the dealer's 10, the basic strategy advises you to draw a card, but in case of a high number of high cards the strategy changes and now you are advised to stand.
There are other card-counting strategies differing from each other in the method of counting aces. This card plays quite an important role in this game (without an ace you cannot have blackjack and it is paid in the ratio 3:2).
Counting cards has no positive impact for a player when playing video blackjack, because all the cards are dealt randomly. This means that each game is played with a new virtual deck of cards. In live blackjack, in a real casino or in an online casino, it is to some extent possible to use card counting to gain an advantage over the casino.
How casinos protect themselves
It should however be noted that casinos are fighting back against card counting. Card counting is a legitimate method of winning over a casino, but when a player is discovered to be practicing this art, the casino has the right to stop the game and prohibit the player's future entrance to the casino.
Casinos protect themselves by using other methods such as using a cut card. In practice this means that only half of the cards are dealt out of eight decks. The cut card is placed into the shoe indicating to the dealer that the game will be completed after the round in progress finishes and the cards will be freshly shuffled. This method significantly reduces the profitability of card counting, as the benefits of card counting are the highest towards the end of a shoe.
Counting cards also loses its meaning if the casino uses a CSM (continuous shuffling machine). CSM is a device for automatic shuffling of cards. Therefore, after the completion of each round, the used cards are shuffled immediately.
Shuffle tracking is a less popular and more demanding strategy to be managed and to be revealed by the casino. The strategy is based on your good eyesight and excellent memory. If you manage to remember which cards have been dealt and trace how they were shuffled, you can gain an advantage. The principle is simple – the player remembers groups of cards, assigns them a value and when a new game is opened, the player decides according to which cards follow.
The strategy can be used provided that the cards are not shuffled by an automatic device, but directly by the dealer. This is the case where human factor may fail and it can result in inconsistent shuffling of cards.