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''This article is about the casino game of blackjack. For other uses of the word see Blackjack (disambiguation).

Blackjack, also known as twenty-one, is one of the most popular casino card games in the world. Much of its popularity is due to the mix of chance with an element of skill and decision making that is involved, and the publicity that surrounds the practice of card counting, in which players can win money by making betting and strategy decisions based on the cards that have been dealt. Casinos strongly frown upon card counting, but it is a difficult skill to master and few players are successful at it.

Table of contents
1 Rules
2 Special plays
3 Basic Strategy
4 Basic Strategy Tables
5 Card Counting
6 Recent developments
7 Other advantageous casino games


In blackjack, the players bet against the house dealer, rather than against each other. The goal of each player is to have a higher point total than the dealer without going over 21. The values of the cards in any given person's hand are added with 2 through 10 having face value, Ace having value 1 or 11, and King, Jack, and Queen cards having the value 10. If the player and the dealer both have the same point value, this is known as a "push", and neither player wins the hand.

After initial bets are placed, the dealer deals out the cards (either from a single hand-held deck of cards, or more commonly from a shoe containing four or more decks): two cards to each player, including himself. One of the dealer's two cards is visible, the other hidden (the hidden card is known as the "hole card"; in European blackjack, the hole card is not actually dealt until the players all play their hands). The cards of the players are dealt either face up or face down, depending on local casino practice; face up is the most common. At this point, if any player has a "natural" 21 (an Ace with any 10-count card), he is immediately paid 3:2 (most of the time: see Basic Strategy below) for his bet, unless the dealer also has a natural, which is a push. If the dealer has a natural, all players without a natual lose immediately; they do not get a chance to further improve their hands.

If the dealer does not have a natural, then one by one the dealer gives each player the option of asking for more cards (called "taking a hit") or staying with his current total (called "standing" or "holding"). The player may continue to ask for more cards, one by one, until he has either gone over 21 ("a bust"), or he is satisfied with the cards that he has. In addition, depending on what cards the player holds, and depending on the rules in effect at the table, the player may have the option of performing certain special plays (described below). If the player busts (takes a hit that put him over 21), he immediately loses the bet. Once all the players have finished making their decisions, the dealer then reveals the hidden "hole" card and may or may not draw additional cards. The decision of whether to draw more cards is not up to the dealer's discretion; it depends only on the point total that the dealer holds. If the dealer has less than 17, he draws another card, and continues to draw more cards until having a value equal to or greater than 17. If the dealer busts, then all remaining players win. Bets are normally paid out at the odds of 1:1. Casino rules vary on whether the dealer takes a hit when holding a "soft" 17 (that is, a hand such as an Ace with a six, which can be counted as either 7 or 17). In Atlantic City, all dealers will stand on a soft 17. In other areas, this is up to the individual casino.

Special plays

Casinos often offer variations on the rules which add to the player's gambling opportunies during the course of play. The most common of these are:

Basic Strategy

As in all casino games, the house has a statistical advantage over the players that will play itself out in the long run. But because blackjack, unlike other games, has an element of player choice, players can actually reduce the casino advantage to just a small percentage by playing what is known as basic strategy. This strategy determines when to hit and when to stand, and also determines when doubling down or splitting is the correct action. Basic strategy is based on the player's point total, and the dealer's visible card. There are slight variations in basic strategy depending on the exact house rules and the number of decks used. Under the most favorable conditions (single deck, downtown Las Vegas rules), the house advantage over a basic strategy player can be as low as 0.16%. Indeed, casinos offering special rules like surrender and double-after-split may actually be offering a positive expectation to basic strategy players; they are counting on players making mistakes to make money.

The following rules are beneficial to the player:

  1. Doubles are permitted on any two-card hand save a blackjack.
  2. Doubles are permitted after splitting.
  3. Early surrender; the ability to forfeit half your wager against a face or ace before the dealer checks for blackjack
  4. Resplitting Aces.
  5. Drawing more than one card against a split Ace.
  6. Five or more card automatic wins ("Charlies")

The follwing rules are detrimental to the player:
  1. Less than 3-2 payout on blackjacks (as is the case with Las Vegas Strip single-deck blackjack, paying out 6:5)
  2. Splitting a maximum of once (two hands)
  3. Double down restricted to certain totals, such as 9-11 or 10,11
  4. Aces may not be resplit
  5. No-Peek (European) blackjack - player loses splits and doubles to a dealer blackjack
  6. Player losing ties

Basic Strategy Tables

Your Hand Dealer's face-up card
Hard totals
Soft totals
The above is a basic strategy table for 1 deck, Las Vegas Strip rules. Key : S=Stand, H=Hit, D=Double, Sp=Split.

(Should add a basic strategy table 4 decks?)

Card Counting

Unlike casino games such as Roulette and Craps where the outcome of one play has no effect on any future play, a hand of blackjack depletes the deck of the cards used in that hand, and this can alter the probability or certain events occurring on the next deal. Specifically, if the remaining cards have a higher proportion of 10-count cards and Aces than normal, it is more likely that a player will be dealt a natural, which is to the player's advantage (yes, it's also more likely for the dealer to get a natural--but the dealer only wins even money, while the player is paid 3:2). When the deck has more small cards like 4s, 5s, and 6s; it is more likely that the player will be dealt a bad hand and bust, favoring the dealer (likewise, they increase the chance of a dealer bust as well, but when the player busts, the dealer wins even if he later busts himself).

Because the house advantage in blackjack is so small to begin with, it is quite common for a deck that happens to be "rich" in 10-counts and Aces to offer a positive expecation to the player on the next hand. By keeping track of the cards played, a player can take advantage of these situations by betting larger amounts when the deck is in his favor, and smaller amounts when it is not. In the long run, the deck will be unfavorable to the player as often as it is favorable, but it is the amount bet under each condition that counts. The player can also use information about the deck's composition to alter strategy. For example, basic strategy calls for hitting a 16 when the dealer's upcard is a 10, but this is a very close play; one loses less by hitting than standing, but not by much. If it is known, however, that the deck is depleted of small cards like 4s and 5s, and rich in 10s, that may alter the odds in favor of standing.

Most card counting schemes assign a positive, negative, or zero point value to the each card in the deck. Normally, low value cards, such as a 2 or 3, are given a positive value, and 10s are given a negaitive value. The exact number assigned to the cards depend on the specific card counting method in use. The card counter keeps a running tally of the point values as they are dealt. In order to make the count an accurate representation of the percentage of "good" cards left in the deck, this running tally must normally be divided by a factor based on the counter's estimate of the number of undealt cards that are left (so-called unbalanced counts, do not require this additional adjustment, because that is factored into the count).

If the tally is a sufficiently high, the counter can increase his or her bet, and also may make modifications to basic strategy. All of these calculations must be accurate, at the same time that the dealer and other players may be talking to him, and it must be done in such a way that the casino does not notice that any counting is taking place, in order to avoid facing casino countermeasures.

In addition, a card counter can play the Insurance bet if the count of faces is sufficiently high with potentially an advantage over the house.

Counting schemes which assign point values of -1, 0, or +1 are called level one counts, and are considered the easiest to perform. Slightly greater accuracy, at the cost of increased difficulty and likelihood of making mistakes, involves the use of multi-level counts, which assign point values of -2, +2, or greater to the various cards. This greater range of point values adds to the complication of keeping an accurate tally in one's head.

A final complication in card counting involves the issue of how to treat aces. Aces can add the lowest possible value of 1 to a player's card total, which implies that they should have a negative point count; but for purposes of getting a blackjack, they are extremely valuable to have remaining in the deck. Most counting schemes give aces a positive count, recognizing that there is a compromise involved in this process. One scheme actually assigns a zero value to aces, and requires the counter to keep a separate side count of aces.

(Need references to Thorpe, Uston, Snyder, etc.)

Casinos can counter card counting by using large numbers of decks in dealing cards or by frequently shuffling the cards. However, casinos dislike this because it reduces the amount of time that the non-card counting players are playing and consequently losing money to the house. Casinos also look out for known card counters, who may be banned from play depending on regulatory commission rules, as well as look for suspicious actions such as a long series of small bets followed by large one.

Many casual card counters make small mistakes that cost the advantage they gain by counting. Two or three mistakes per hour may give back all of the counter's advantage. Even if you can count perfectly when practicing at home, it is much more difficult in an actual casino. The Nevada casinos only ban the really skilled counters playing for medium or high stakes; other states' casinos lack the ability to bar players, and may alter the game's dynamic against card counters by raising the minimum or lowering the limit on a table with a suspected counter, or by reshuffling sooner than the normal end of the shoe if they think that the player is offering a large bet on a positive count. (In these states, only the state gaming regulatory commission has the ability to bar people from casinos. Nevada also maintains such a list, and these lists are often shared amongst the various casinos and state regulators.)

There have been some high-profile lawsuits involving whether or not the casino is allowed to bar card-counters. Essentially, card-counting, if done in your head and with no outside assistance with devices or additional people, is not illegal (they can't arrest anyone for working in their own head). Using an outside aid, though, is illegal. However, the casinos really dislike counters, and if permitted by their juristiction may ban you from their casino; in Nevada, where the casinos are ruled to be private places, the only prerequisite to a ban is the full reading of the Trespass Act to ban you for life. Some really skilled counters try to disguise their identities and playing habits; however, facial recognition software in use by casinos can often match up a camouflaged face with a banned one.

Most casinos now hire a consulting firm to help them track/discipline card counters.

Recent developments

Both basic strategy and card counting are based on the assumption that cards are dealt at random. In 2002 Ben Mezrich published the book Bringing Down the House in which he claimed that he and others exploited non-randomness in the shuffling of cards to develop a strategy superior to conventional card counting.

Other advantageous casino games

The other casino games where a player can get an advantage is on certain advantageous video poker machines, especially when there is a large progressive jackpot, and regular poker tables, where the players wager against each other instead of the house and a skilled player can win with more frequency.