Blackjack, also known as Twenty-one or Vingt-et-un (French for "twenty-one"), is a comparing-type card game which is the most widely played casino banking game in the world. The standard game is played with one or more Anglo-American decks  of 52 cards. The player draws cards to an initial two card hand with the object of bringing the total hand value as close as possible to 21 without exceeding it, so that the house, which plays after the player, will fail to get up to the player's total, or will lose by exceeding 21.

Blackjack is played in many variations at casinos with different table rules. Much of blackjack's popularity is due to the mix of chance, skill, and the publicity that surrounds card counting, which entails adapting one's wager and playing strategy to the profile of cards yet to be dealt.

Blackjack is closely related to the games of Spanish 21 and Pontoon, but unrelated to the British game with the similar name Black Jack which is a shedding-type card game.

History of BlackJack

Blackjack's precursor was Twenty-one, a game of unknown origin. The first written reference is found in a book by the Spanish author Miguel de Cervantes, who is most famous for writing Don Quixote. Cervantes was a gambler, and the main characters of his tale "Rinconete y Cortadillo", from "Novelas Ejemplares", are a couple of cheaters working in Seville. They are proficient at cheating at "ventiuna" (Spanish for twenty-one), and state that the object of the game is to reach 21 points without busting and that the ace values 1 or 11. The game is played with the Spanish baraja deck, which lacks eights, nines and tens. This short story was written between 1601 and 1602, implying that the ventiuna was played in Castilia since the beginning of the 17th Century or earlier. Later references to this game are found in France and Spain.

When Twenty-one was introduced in the United States, it was not popular, so gambling houses tried offering various bonus payouts to get the players to the tables. One such bonus was a ten-to-one payout if the player's hand consisted of the ace of spades and a black jack (either the jack of clubs or the jack of spades). This hand was called a "blackjack" and the name stuck to the game, even though the bonus payout was soon abolished. In the modern game, a "natural" or "blackjack" is simply an ace plus a ten-value card.

BlackJack Rules

In blackjack at a casino, the dealer faces between five and nine (commonly seven) playing positions from behind a semicircular table. Each position may be occupied by up to three players. A single player is often permitted to control or bet on as many positions as desired. At the beginning of each round, bets are placed in the "betting box" at each position in play. The player whose bet is at the front of the betting box is deemed to have control over the position, and the dealer will consult the controlling player for playing decisions regarding the hand. Each wagered-on position is dealt an initial hand of two cards visible to the player of that box, and often to any other players. The dealer receives a single face up card, and in some games draws a second card, concealed from the players (the "hole" card, used to establish immediately whether the dealer has blackjack). In European casinos, the dealer's second card is neither drawn nor consulted until the players all play their hands.

Cards are dealt either from one or two hand-held decks, from a dealer's shoe, or from a shuffling machine. Single cards are dealt to each of wagered-on position clockwise from the dealer's leftmost position, followed by a single card to the dealer, followed by an additional card to each of the positions in play. The players' initial cards may be dealt face-up, or face-down (more common in single-deck games).

The players' object is to win money by getting a card total which will turn out to be higher than the dealer's hand, but without exceeding 21 ("busting"/"breaking"), and taking advantage of certain opportunities which arise within the play to increase the wager. Each hand is played by choosing whether to "hit" (take a card), "stand" (pass), "double" (double wager, take a single card and pass), "split" (make two hands out of a pair) or "surrender" (give up a half-bet and retire from the game). Number-cards count as their natural value; the jack, queen, and king (also known as "face cards" or "pictures") count as 10; aces are valued as either 1 or 11 according to the player's best interest. If the hand value exceeds 21 points, it busts, and its bet is immediately forfeit. After all boxes have finished playing, the dealer's hand is resolved by drawing cards until the hand busts or achieves a value of 17 or higher (a dealer total of 7 including an ace, or "soft 17", must be drawn to in some games). The dealer never doubles, splits nor surrenders. If the dealer busts, all remaining bets win and are paid out at 1:1. If the dealer does not bust, each remaining bet wins if its hand is higher than the dealer's, and loses if it is lower. In the case of a tied score, known as "push" or "standoff", the bet is normally returned without adjustment.

The best possible hand is a "blackjack" or "natural", which is an ace and a ten-value card in either order on the initial two cards (not after a split). A blackjack beats any hand which is not a blackjack, even those with value 21. Blackjack vs. blackjack is a push. When the dealer's upcard is an ace, the player is usually allowed to make a side bet called "insurance," of up to half his wager, which pays 2:1 if the dealer gets a blackjack, and is forfeited otherwise.

The minimum and maximum bets are posted on the table. The payoff on most bets is 1:1, meaning that the player wins the same amount as he or she bets. The traditional payoff for a player blackjack is 3:2, meaning that the casino pays $3 for each $2 originally bet, but many casinos today pay less at some tables.

Player decisions

After receiving his initial two cards, the player has four standard options: he can "hit," "stand," "double down," or "split a pair." Each option requires the use of a hand signal. At some casinos or tables, the player may have a fifth option, called a "surrender."

* Hit: Take another card from the dealer.

signal: (handheld) Scrape cards against table. (face up) Touch finger to table or wave hand toward himself or herself.

* Stand: Take no more cards; also known as "stand pat", "stick", or "stay".

signal: (handheld) Slide cards under chips. (face up) Wave hand horizontally.

* Double down (only available as first decision of a hand): The player is allowed to increase the initial bet by up to 100% in exchange for committing to stand after receiving exactly one more card. The additional bet is placed in the betting box next to the original bet. Some games do not permit the player to increase the bet by amounts other than 100%. Non-controlling players may double their wager or decline to do so, but they are bound by the controlling player's decision to take only one card.

signal: Place additional chips next to (not on top of) the original bet. Point with one finger.

* Split a pair (only available as first decision of a hand): If the first two cards are a "pair" (of the same denomination), the player can split them into two hands, by moving a second bet equal to the first into an area outside the betting box of the original bet. The dealer separates the two cards and draws a further card on each, placing one bet with each hand. The player then plays out the two separate hands in turn, with some restrictions. In the case of ten-valued cards, some casinos allow splitting only when the cards have the identical symbols; for instance, a hand of T-T or K-K may be split, but not of T-K or K-T. Other casinos allow splitting of any pair of ten-valued cards. Common restrictions on playing hands which originate from a split relate to doubling, re-splitting, blackjack and hitting split aces. Non-controlling players may follow the controlling player by putting down an additional bet, or decline to do so, instead associating their existing wager with one of the two spawned hands. In that case they must choose which hand to play behind before the second cards are drawn.

signal: Place additional chips next to the original bet outside the betting box. Point with two fingers spread into a V formation.

* Surrender (only avaliable as first decision of a hand): Some games offer the option to "surrender." After the dealer has checked for blackjack, the player may "surrender", whereupon the house will take half the player's bet and return the other half to the player; this terminates the player's interest in the hand. The request to surrender is made verbally, there being no commonly accepted hand signal.

Hand signals are used to assist the "eye in the sky," a person or video camera located above the table and sometimes concealed behind one-way glass. The recording provides a means of resolving disputes or identifying mistakes, and is also used to protect the casino against dealers who steal chips or players who cheat. It may also be used by the casino to identify advantage players whose activities, while legal, make them undesirable customers.

Each player may normally "hit" as many times as desired so long as the total in his hand is not above hard-20. On achieving 21 (including soft 21), a player is normally required to stand; busting is an irrevocable loss and the player's wager is immediately forefeited to the house. After a bust or a stand, play proceeds to the next player clockwise around the table. When the last player has finished, the dealer then reveals the hole card and stands or draws further cards according to the rules of the game. After the dealer's final outcome is established, any bets remaining on the table associated with losing hands are forefeited, and winners are paid out.

Insurance

If the dealer's upcard is an ace, the player is offered the option of taking "insurance" before the dealer checks the hole card.

Insurance is a side bet that the dealer has blackjack, available when the dealer's exposed card is an ace. The idea is that the dealer's second card has a fairly high probability (nearly one-third) to be ten-valued, giving the dealer a blackjack and almost certainly results in a loss for the player. Up to half the original bet may be wagered on insurance, and the insurance wager is placed on a special portion of the table usually marked "Insurance Pays 2 to 1". A player who himself has a blackjack may also take insurance. A player with blackjack taking out maximum insurance is guaranteed a total payout equal to his main wager, whether or not the dealer has blackjack; in this circumstance insurance may be referred to as "even money" and paid out before the hand is resolved, obviating the need for the player to provide a material insurance wager. It is attractive (although not necessarily wise) for the player to insure against this possibility by making a maximum "insurance" bet, in which case the "insurance proceeds" will make up for the concomitant loss on the original bet. The insurance bet is lost if the dealer does not have blackjack, although the player can still win or lose on the original bet. The worst case for an insured player is when the dealer does not achieve blackjack, but subsequently achieves 21 in three or more cards.

On average, insurance costs the player money. In an infinite deck, 4/13 of the cards have a value of ten (10, J, Q, or K) and 9/13 therefore are not, so the theoretical return for an infinite deck game is 4/13 * 2 * bet - 9/13 * bet = -1 /13 * bet, or -7.69%. In practice, the average house edge will be lower than this, because by eliminating even one non-ten card from the shoe (the dealer's ace), the dealer causes the proportion of the remaining cards that are valued at ten to be higher. Even so, house's average edge is still more than 7%, and as a result most authorities advise against it. However the insurance outcome is strongly anti-correlated with that of the main wager, and if the player's priority is to reduce variation, it is reasonable to pay for this.

The insurance bet is susceptible to card counting. By keeping track of the remaining tens in the shoe, a player can identify exactly when making insurance bets is advantageous, which is the case if more than one third of the remaining cards are tens. Indeed, in a multi-hand single deck game, it is possible for insurance to be a good bet if the player simply observes the other cards on the table - for an initial hand, if the dealer has an ace, then there are 51 cards left in the deck, of which 16 are tens. However, if there are as few as 2 players playing, and neither of their two initial cards is a ten, then 16 of 47 remaining cards are tens - better than 1 in 3, making the insurance bet a good one. Advantageous even-money bets are slightly rarer, since the ten in the player's blackjack makes it less likely that the dealer has blackjack too.

Hole card games ares sometimes played on tables with a small mirror or electronic sensor which the dealer can use to check for blackjack without inadvertently revealing the hole card.

Rule variations and their consequences for the house edge

While the basic rules of casino blackjack are generally determined by law or regulation, certain variations are allowed at the discretion of the casino. The key game rules are generally posted on or near the table, failing which there is an expectation that casino staff will provide them on request. Over 100 variations of blackjack have been documented.

As with all casino games, blackjack incorporates a "house advantage" or "house edge". The primary house advantage in blackjack comes from the fact that if the player busts he loses, regardless of whether the dealer subsequently busts. Nonetheless, a blackjack player using basic strategy will lose less than 1% of his total wagered amount with strictly average luck; this is very favorable to the player compared to other casino games. The loss rate of players who deviate from basic strategy through ignorance is in general expected to be greater.

Dealer hits soft 17

Each game has a rule about whether the dealer must hit or stand on soft 17, which is generally printed on the table surface. The variation where the dealer must hit soft 17 is abbreviated "H17" in blackjack literature, with "S17" used for the stand-on-soft-17 variation. Substituting an "H17" rule with an "S17" rule in a game benefits the player, decreasing the house edge by about 0.2%.

Number of decks

All things being equal, using fewer decks decreases the house edge. This mainly reflects an increased likelihood of player blackjack, since if the player draws a ten on his first card, the subsequent probability of drawing an ace is higher with fewer decks. It also reflects a decreased likelihood of blackjack-blackjack push in a game with fewer decks.

Casinos generally compensate by tightening other rules in games with fewer decks, in order to preserve the house edge. When offering single deck blackjack games, casinos are more likely to disallow doubling on soft hands or after splitting, to restrict resplitting, and to pay the player less than 3:2 for a winning blackjack.

The following table illustrates the mathematical effect on the house edge of the number of decks, by considering games with various deck counts under the following ruleset: double after split allowed, resplit to four hands allowed, no hitting split aces, no surrender, double on any two cards, original bets only lost on dealer blackjack, dealer hits soft 17, and cut-card used. The increase in house edge per unit increase in the number of decks is most dramatic when comparing the single deck game to the two-deck game, and becomes progressively smaller as more decks are added.

Late/early surrender

Surrender, for those games that allow it, is usually first permitted only after the dealer has checked the hole card for blackjack and is therefore referred to as "late" surrender. The alternative, "early" surrender, gives the option for the player to surrender before the dealer checks for blackjack or in a no-hole-card game. Early surrender was originally the norm in Atlantic City casinos but is much more favourable to the player than late surrender, and has largely disappeared. Nonetheless early surrender games can still be found in several countries. Most medium-strength hands should be surrendered against a dealer Ace if the hole card has not been checked.

While it is tempting opt for surrender on any hand which will probably lose, the correct strategy is to only surrender on the very worst hands, because having even a 25% chance of winning the full bet is better than losing half the bet and pushing the other half, as entailed by surrendering.

Resplitting

If the player splits a pair, and one or both of the the newly formed hands are also a pair, most games allow the player to split any new pairs (or "resplit"). The player places a further wager and the dealer separates the new pair dealing a further card to each as before. Some games allow unlimited resplitting, while others may limit it to a certain number of hands, such as four hands (for example, "resplit to 4"). It is common for resplitting to be specifically prohibited in the case of aces, but allowed for other denominations.

Hit/resplit split aces

After splitting aces, one common rule is that only one card will be dealt to each ace; the player cannot split, double, or take another hit on either hand. Rule variants include allowing resplitting aces or allowing the player to hit split aces. Allowing the player to hit hands resulting from split aces reduces the house edge by about 0.13%; allowing resplitting of aces reduces house edge by about 0.03%. While games allowing aces to be resplit are not uncommon, those allowing the player to hit split aces are extremely rare.

Double after split

After a player has split a pair, most casinos allow doubling down on the new two-card hands. "Double after split" decreases the house edge by about 0.12%.

Double on 9/10/11 or 10/11 only

This rule, often called the Reno rule, restricts the player to doubling down only on an initial player total of 10 or 11 (sometimes 9, 10, or 11 - more common in Europe). It prevents doubling on soft hands such as soft 17 (ace-6), and is unfavorable for the player. It increases the house advantage by between 0.09% (8 decks) and 0.15% (1 deck) for the 9-11 rule, and between 0.17% (8 decks) and 0.26% (single deck) for the 10-11 rule. These numbers can vary due to interaction with other rules.

No hole card and OBO

In most non-U.S. casinos, a 'no hole card' game is played, meaning that the dealer does not draw nor consult his second card until after all players have finished making decisions. With no hole card, it is almost never correct basic strategy to double or split against a dealer ten or ace, since a dealer blackjack will result in the loss of the split and double bets; the only exception is with a pair of A's against a dealer 10, where it is still correct to split. In all other cases, a stand, hit or surrender is called. For instance, holding 11 against a dealer 10, the correct strategy is to double in a hole card game (where the player knows the dealer's second card is not an ace), but to hit in a no hole card game. The no hole card rule adds approximately 0.11% to the house edge.

The "original bets only" rule variation appearing in certain no hole card games states that if the player's hand loses to a dealer blackjack, only the mandatory initial bet ("original") is forfeited, and all optional bets, meaning doubles and splits, are pushed. "Original bets only" is also known by the acronym OBO; it has the same effect on basic strategy and house edge as reverting to a hole card game.

Altered payout for blackjack

In many casinos, usually at tables with the lowest table minimums and single-deck games, a blackjack pays only 6:5 or even 1:1 instead of the usual 3:2. Among common rule variations in the U.S., these altered payouts for blackjack are the most damaging to the player, causing the greatest increase in house edge. Since blackjack occurs in approximately 4.8% of hands, the 1:1 game increases the house edge by 2.3%, while the 6:5 game adds 1.4% to the house edge. Video blackjacks generally pay 1:1 payout for blackjack, and this is a key reason why it has never approached the table version in terms of popularity (as well as the fact that cards are shuffled after every deal, which renders counting schemes much less effective). The 6:5 rule is most commonly employed on table blackjack at single deck games, where they help the house to compensate for low house edge intrinsic in using one deck only.

Dealer wins ties

The rule that bets on tied hands are lost rather than pushed is catastrophic to the player.[citation needed] Though rarely used in standard blackjack, it is sometimes seen in "blackjack-like" games such as in some charity casinos.

Basic Blackjack Strategy

The complete set of optimal decisions for a player regarding only the dealer's current exposed card and the point total of his own current hand is known as basic strategy. The basic strategy table below applies to the following ruleset:




* 4 to 8 decks
* Dealer stands on soft 17
* Double on any 2 cards
* Double after split allowed
* Only original bets lost on dealer blackjack
* Late surrender




Key:

  S  = Stand
  H  = Hit
  Dh  = Double (if not allowed, then hit)
  Ds  = Double (if not allowed, then stand)
  SP  = Split
  SU  = Surrender (if not allowed, then hit except stand on 16v10 if not first two cards.)

In most Las Vegas Strip casino games, the dealer must hit on soft 17. This rule change requires a slightly modified basic strategy table: double on 11 vs. A, double on A/7 vs. 2, double on A/8 vs. 6 and surrender 15, 17 or 8/8 vs. A.

Composition-dependent strategy

Basic strategy is based upon a player's point total and the dealer's visible card. A player may be able to improve on this decision by considering the precise composition of his hand, not just the point total. For example, a player should ordinarily stand when holding 12 against a dealer 4. However, in a single deck game, the player should hit if his 12 consists of a 10 and a 2. The presence of a 10 in the player's hand has two consequences:

* It makes the player's 12 a worse hand to stand on (since the only way to avoid losing is for the dealer to go bust, which is less likely if there are fewer 10's left in the shoe).
* It makes hitting safer, since the only way of going bust is to draw a 10, and this is less likely with a 10 already in the hand.

However, in situations in which basic and composition-dependent strategy lead to different actions, the difference in expected value between them is small. Additionally, as the number of decks used in a blackjack game rises, both the number of situations in which composition determines the correct strategy and the house edge improvement from using a composition-dependent strategy falls. Using a composition-dependent strategy only reduces house edge by 0.0031% in a six-deck game, less than one tenth the improvement in a single-deck game (0.0387%).

Advantage play

Blackjack has been a pre-eminent target in casinos for several decades in the field of advantage play, which is the attempt to win more using "honest" skills such as memory, mental computation and observation. These techniques, while entirely legal, can be powerful enough to give the player a long-term edge in the game, making them an undesirable customer for the casino and leading to ejection or blacklisting if they are detected. The main techniques of advantage play in blackjack are as follows:

Card counting

During the course of a blackjack game, the dealer progressively exposes cards which are dealt to his own and the players' hands. Careful observation of the exposed cards allows a player to make inferences about the cards which remain to be dealt, and use these inferences in one of two ways:

* The player can make larger bets when he has the advantage. For example, the player can increase the starting bet if there are many aces and tens left in the deck, in the hope of hitting a blackjack.
* The player can deviate from basic strategy according to the composition of his or her undealt cards. For example, with many tens left in the deck, the player may double down in more situations since there is a better chance of getting a good hand.

A typical card-counting system applies a point score for each rank of card (e.g. 1 point for 2-6 , 0 points for 7-9 and -1 point for 10-A). Whenever a card is exposed, a counter adds the score of that card to his running total score, which is used to make betting and playing decisions according to a table which he has learned. The count starts at 0 for a freshly shuffled deck for "balanced" counting systems. Unbalanced counts are often started at a number which reflects the total number of decks.

Depending on the particular blackjack rules in a given casino, basic strategy reduces the house advantage to less than 1%. Card-counting, if done correctly, can give the player an advantage, typically ranging from 0 to 2% over the house.

Card-counting is most rewarding near the end of a complete shoe when as few as possible cards remain. Single-deck games are therefore particularly susceptible to card counting. As a result, casinos are more likely to insist that players do not reveal their cards to one another in single-deck games. In games with more decks of cards, casinos limit penetration by ending the shoe and initiating a reshuffle when one or more decks remain undealt, or by using a shuffling machine to reintroduce the exhausted cards every time a deck has been played.

Card-counting mentally is legal and is not considered cheating. However, most casinos have the right to ban players, with or without cause, and card-counting is frequently a reason for banning a player. Usually, the casino will inform the player that he is no longer welcome to play blackjack at that casino and he or she may be banned from the property. Players must be careful not to signal the fact that they are counting, and the use of electronic or other counting devices is usually illegal.

Shuffle tracking

Techniques other than card-counting can swing the advantage of casino blackjack toward the player. All such techniques are based on the value of the cards to the player and the casino, as originally conceived by Edward O. Thorp. One technique, mainly applicable in multi-deck games, involves tracking groups of cards (aka slugs, clumps, packs) during the play of the shoe, following them through the shuffle and then playing and betting accordingly when those cards come into play from the new shoe. Shuffle tracking requires excellent eyesight and powers of visual estimation, but is more difficult to detect since the players actions are largely unrelated to the composition of the cards in the shoe.

Arnold Snyder's articles in Blackjack Forum magazine brought shuffle tracking to the general public. His book, The Shuffle Tracker's Cookbook, mathematically analyzed the player edge available from shuffle tracking based on the actual size of the tracked slug. Jerry L. Patterson also developed and published a shuffle-tracking method for tracking favorable clumps of cards and cutting them into play and tracking unfavorable clumps of cards and cutting them out of play.

Other legal methods of gaining a player advantage at blackjack include a wide variety of techniques for hole carding or gaining information about the next card to be dealt. In addition, match-play coupons give the skillful basic-strategy blackjack player an edge. And finally, a special promotion - such as 2:1 for a blackjack - can temporarily swing the advantage to the player.