Everything about Tracking Decks at Blackjack

Track the Deck: The Art of Counting at 21

In the game known as “21” or Blackjack, the odds of winning change every time a card is removed from the deck. For example, the probability of being dealt an Ace from a fresh deck of 52 cards is 4:52 or 7.7%. But once an Ace has been drawn and removed, the chances of being dealt a second Ace drop to 3:51 or 5.9%. And of course, when all four Aces have been dealt, the odds of another Ace appearing fall to zero—none whatsoever.

When a deck contains fewer Aces than the starting percentage, 7.7%, it is referred to as “Ace poor.” But when it contains a higher percentage than that, it is said to be “rich” in Aces. Since Aces are cards highly desired by players of 21, those who know when a deck is rich or poor can vary their wagering accordingly to take advantage of the situation. And keeping track of face cards, tens and other important cards can serve a similar purpose.

That explains why “card counting” has received so much attention in the past 50 years.

The Art of Counting at 21

Card counting provides a method of keeping track of cards that have been played, identifying how “rich” or “poor” decks are and how that affects the odds. Card counters are thus able to know when the cards remaining in the deck favor the player, and a number of popular counting strategies have been developed toward this end, such as the following:

Five Count Strategy

Calculations have shown that removing all of the fives from a deck of 52 cards gives the player a 3.04% advantage over the house. And tracking fives is relatively easy, because one should appear among every 13 cards. When sitting at a table of six players plus the dealer, there are 14 cards dealt at the start of each hand, of which thirteen are visible. If no five appears, the deck is rich in fives. If one five appears, it is about even. And if two or more fives come up, the deck is poor and ready for a larger wager on the next hand.

Plus/Minus Strategy (aka High-Low Count)

Whenever high cards (Ace~Ten) are removed from the deck, the House edge improves. On the other hand, decks lacking low cards (Two~Six) favor the player. This system of counting assigns the low cards +1 point apiece as they are removed from the deck. The high cards are worth -1 point each as they are played. Middle cards (Seven~Nine) count as zero and are ignored. The Count starts at zero and when it reaches +2 or higher in a single deck game, the deck is rich in high cards and wagers should be increased. For multi-deck games, a favorable Count is +5 or higher.

Ten Count Strategy

There are a number of variations on this strategy, but all of them require the player to keep track of a ratio. It is the number of cards valued at ten to the number of all other cards played. A fresh deck contains 16 tens and 36 non-tens, or a ratio of 4:9. When the ratio is lower than this, the deck is rich in tens and betting should be increased. The threshold for doing so can be found in a chart indicating favorable ratios at 0:4, 1:6, 2:8, 3:10; 4:12; 5:14 and so on.

Point Count Strategy

Much like the Plus/Minus Strategy, this counting system assigns a value to each card as it played as follows: Twos and Sevens are worth +1 point each; cards Three~Six count as +2 points; Eights and Nines are worth zero and ignored; and cards Ace~Ten are valued at -2 points as they are removed from the deck. Again, the Count starts at zero. When it is positive, the deck favors the player; when it is negative, it benefits the dealer, so wager accordingly.