Card counting is a strategy principally used in the casino game blackjack. The system determines odds for player wins or house advantage. Card counting is a statistical tool effective in helping a player to keep track of density of cards over the course of a game of blackjack. Ideally, a higher density of high cards puts the player at a higher advantage for placing a higher bet. More low cards give the casino a high advantage. The beauty of card counting lies in the fact that you can alter bets depending on density of remaining cards as the game progresses.
The basic counting approach relies on a system of assigning a (-)ve, (+)ve, or (0) value to each card value available. Dealing a card of that value adjusts a card to its counting value. There are several card counting systems, ranging from very simple strategies that favour beginners to highly complex systems for experienced players. The most common among the level 1 (simple) is the Hi-Lo system, preferred for its accuracy. Other systems include the KISS, Knock out blackjack and the Red 7.
In the Hi-Lo system, all cards give a count of zero. A negative count means there are more low cards and the opposite is true for a positive count. The system subtracts 1 for each 10, King, Queen or Ace dealt and adds 1 for values between 2 and 6. Values between 7 and 9 are assigned zero and do not have an impact on the count. A high density of 10s and Aces is the player’s advantage as it implies a higher chance of smashing a natural blackjack with a 3:2 payout unless the house also has a blackjack.
The hi-lo approach is considered a basic system as the running count changes by a single predetermined value. Others like the Wong Halves and Zen count are multi-level counting mechanisms and are thus more accurate. Mid-level systems (level 2 and 3) like Omega II assign +2 and -2 values to cards and are considered more accurate than level 1 systems.
Your level of experience will determine which approach works to your advantage.