Card Counting in blackjack: Can you really gain an advantage over the casino?

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Card Counting is a method used in blackjack by players aiming to give themselves an advantage over the casino. In blackjack playing a perfect strategy (i.e. making the best decisions every time) without any card counting, still gives the casino an edge of around 0.5%. However, card counting can give the player an edge over the casino upto 2%.

Why does card counting give the player an edge?

By keeping track of the high and low cards already dealt to the player / other players / dealer during this and previous hands, it is possible to understand whether the remaining cards are high / low / neutral. In blackjack high cards are good for the player, whilst low cards are not. The card counter will bet (or place bigger bets) when they calculate they have the advantage (i.e. the more high cards left the better), and avoid betting (or place smaller bets) when they calculate the casino has the advantage (when the remaining cards are mostly low). Understanding information about the remaining cards, also allows the card counter to make better decisions during each hand.

The reason higher cards are favourable to the player is players are paid out at 1-1 (evens) if they win. However, if they make a blackjack (also called a natural) these can pay out at 3-2 (this will be less at some casinos). Obviously the possibility of hitting a blackjack, is higher if there are more high cards left in the deck. Doubling down (doubling you wager, before taking exactly one more card) is more likely to be successful in certain situations. Insurance bets (which otherwise should be avoided) might be a profitable bet. Insurance bets pay out at 2-1, and can be made whenever the dealer shows an ace as their first card. As the payout is 2-1, if from your card count you know the dealer’s 2nd card has a better than 1 in 3 chance of being worth 10 points, this bet will be a profitable bet in the long run. Also high cards might mean the dealer is more likely to bust than the player, as the dealer has to take a card based on predetermined rules, which the player can choose not to take a card even when they would have had it not been for their knowledge of the card count). Furthermore, more splits may be possible.

Hi-Lo card counting system

There are many different systems for card counting, and there is no need to keep track of the actual cards dealt – a basic system called the hi-lo system.

How to use the H-Lo card counting system. Start the count at 0.

  1. Deduct 1 from the count

    …for every 10/J/Q/K/A dealt

  2. Add 1 to the count

    …for every 6/5/4/3/2 dealt

  3. Do nothing

    …for any other cards dealt

In the hi-lo system the running count never increases or decreases by more than the same number (and is classified as a level 1 count). This type of count is the easiest to do without much effort required, or the possibility of making mistakes. There are more advanced systems, such as higher level counts, which involve adding/subtracting different numbers based on the cards dealt. Even if these counts could produce more accurate results, you need to take account of the possibility of making errors might also increase if your method becomes more complicated.

Countermeasures casino use against card counting

The fewer cards that remain in the deck, the better idea, the card counter will have about the remaining cards. This means single-deck games are ideal for card counters, who can make increasingly accurate decisions as more and more cards are used up. Casinos can use multiple decks shuffled together, and reshuffling whilst perhaps the equivalent of one deck remains un-dealt, to avoid the card counter having this advantage.

The legality of card counting is dependent on local laws – however generally, unless technology is being used it is not illegal. However, casinos may ban players from blackjack (or even altogether) if they believe they are card counters – this ban might involve blacklisting from other casinos too.