Blackjack

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Blackjack is the American variant of a globally popular banking game known as Twenty-One,  is a comparing card game between one or more players and a dealer, where each player in turn competes against the dealer. Players do not compete against each other. It is played with one or more decks of 52 cards, and is the most widely played casino banking game in the world. The objective of the game is to beat the dealer in one of the following ways:

  • Get 21 points on the player’s first two cards (called a “blackjack” or “natural”), without a dealer blackjack;
  • Reach a final score higher than the dealer without exceeding 21; or
  • Let the dealer draw additional cards until their hand exceeds 21 (“busted”).

Players are each dealt two cards, face up or down depending on the casino and the table at which they sit. In the U.S., the dealer is also dealt two cards, normally one up (exposed) and one down (hidden). In most other countries, the dealer receives one card face up. The value of cards two through ten is their pip value (2 through 10). Face cards (Jack, Queen, and King) are all worth ten. Aces can be worth one or eleven. A hand’s value is the sum of the card values. Players are allowed to draw additional cards to improve their hands. A hand with an ace valued as 11 is called “soft”, meaning that the hand will not bust by taking an additional card; the value of the ace will become one to prevent the hand from exceeding 21. Otherwise, the hand is “hard”.

Once all the players have completed their hands, it is the dealer’s turn. The dealer hand will not be completed if all players have either busted or received blackjacks. The dealer then reveals the hidden card and must hit until the cards total 17 or more points. (At most tables the dealer also hits on a “soft” 17, i.e. a hand containing an ace and one or more other cards totaling six.) Players win by not busting and having a total higher than the dealer, or not busting and having the dealer bust, or getting a blackjack without the dealer getting a blackjack. If the player and dealer have the same total (not counting blackjacks), this is called a “push”, and the player typically does not win or lose money on that hand. Otherwise, the dealer wins.

Blackjack has many rule variations. Since the 1960s, blackjack has been a high-profile target of advantage players, particularly card counters, who track the profile of cards that have been dealt and adapt their wagers and playing strategies accordingly.

Blackjack has inspired other casino games, including Spanish 21 and pontoon.

Rules of play at casinos

Blackjack example game
Initial deal
Player action
Dealer’s hand revealed
Bets settled

At a casino blackjack table, the dealer faces five to seven playing positions from behind a semicircular table. Between one and eight standard 52-card decks are shuffled together. At the beginning of each round, up to three players can place their bets in the “betting box” at each position in play. That is, there could be up to three players at each position at a table in jurisdictions that allow back betting. 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; the other players of that box are said to “play behind”. Any player is usually allowed to control or bet in as many boxes as desired at a single table, but it is prohibited for an individual to play on more than one table at a time or to place multiple bets within a single box. In many U.S. casinos, however, players are limited to playing two or three positions at a table and often only one person is allowed to bet on each position.

The dealer deals cards from his/her left (the position on the dealer’s far left is often referred to as “first base”) to his/her far right (“third base”). Each box is dealt an initial hand of two cards visible to the people playing on it, and often to any other players. The dealer’s hand receives its first card face up, and in “hole card” games immediately receives its second card face down (the hole card), which the dealer peeks at but does not reveal unless it makes the dealer’s hand a blackjack. Hole card games are sometimes played on tables with a small mirror or electronic sensor that is used to peek securely at the hole card. In European casinos, “no hole card” games are prevalent; the dealer’s second card is neither drawn nor consulted until the players have all played their hands.

Cards are dealt either from one or two handheld decks, from a dealer’s shoe, or from a shuffling machine. Single cards are dealt to each wagered-on position clockwise from the dealer’s left, 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 creating card totals that turn out to be higher than the dealer’s hand but do not exceed 21 (“busting”/”breaking”), or alternatively by allowing the dealer to take additional cards until he/she busts. On their turn, players must choose whether to “hit” (take a card), “stand” (end their turn), “double” (double wager, take a single card and finish), “split” (if the two cards have the same value, separate them to make two hands) 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 choice. If the hand value exceeds 21 points, it busts, and all bets on it are 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 17 including an ace, or “soft 17”, must be drawn to in some games and must stand in others). The dealer never doubles, splits, or surrenders. If the dealer busts, all remaining player hands win. 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. If a player receives 21 on the 1st and 2nd card it is considered a “natural” or “blackjack” and the player is paid out immediately unless dealer also has a natural, in which case the hand ties. In the case of a tied score, known as “push” or “standoff”, bets are normally returned without adjustment; however, a blackjack beats any hand that is not a blackjack, even one with a value of 21. Wins are paid out at 1:1, or equal to the wager, except for player blackjacks which are traditionally paid at 3:2 (meaning the player receives three dollars for every two bet) or one-and-a-half times the wager. Many casinos today pay blackjacks at less than 3:2 at some tables; for instance, single-deck blackjack tables often pay 6:5 for a blackjack instead of 3:2.

Blackjack games almost always provide a side bet called insurance, which may be played when dealer’s upcard is an ace. Additional side bets, such as “Dealer Match” which pays when the player’s cards match the dealer’s up card, are sometimes available.

Player decisions

After receiving an initial two cards, the player has up to four standard options: “hit”, “stand”, “double down”, or “split”. Each option has a corresponding hand signal. Some games give the player a fifth option, “surrender”.

  • Hit: Take another card from the dealer.
Signal: Scrape cards against table (in handheld games); tap the table with finger or wave hand toward body (in games dealt face up).
  • Stand: Take no more cards, also known as “stand pat”, “stick”, or “stay”.
Signal: Slide cards under chips (in handheld games); wave hand horizontally (in games dealt face up).
  • Double down: 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 beside the original bet outside the betting box, and point with one finger.
  • Split: If the first two cards of a hand have the same value, the player can split them into two hands, by moving a second bet equal to the first into an area outside the betting box. The dealer separates the two cards and draws an additional card on each, placing one bet with each hand. The player then plays out the two separate hands in turn; except for a few restrictions, the hands are treated as independent new hands, with the player winning or losing their wager separately for each hand. Occasionally, in the case of ten-valued cards, some casinos allow splitting only when the cards have the identical ranks; for instance, a hand of 10-10 may be split, but not one of 10-king. However, usually all 10-value cards are treated the same. Doubling and further splitting of post-split hands may be restricted, and an ace and ten value card after a split are counted as a non-blackjack 21. Hitting split aces is usually not allowed. 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 post-split hands. In that case they must choose which hand to play behind before the second cards are drawn. Some casinos do not give non-controlling players this option, and require that the wager of a player not electing to split remains with the first of the two post-split hands.
Signal: Place additional chips next to the original bet outside the betting box; point with two fingers spread into a V formation.
  • Surrender (only available as first decision of a hand): Some games offer the option to “surrender” directly after the dealer has checked for blackjack (see below for variations). When the player surrenders, the house takes half the player’s bet and returns the other half to the player; this terminates the player’s interest in the hand.
Signal: The request to surrender is made verbally, there being no standard 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 eye in the sky usually makes a video recording of the table, which helps in resolving disputes and identifying dealer mistakes, and is also used to protect the casino against dealers who steal chips or players who cheat. The recording can further be used to identify advantage players whose activities, while legal, make them undesirable customers. In the event of a disagreement between a player’s hand signals and their words, the hand signal takes precedence. Each hand may normally “hit” as many times as desired so long as the total is not above hard 20. On reaching 21 (including soft 21), the hand is normally required to stand; busting is an irrevocable loss and the players’ wagers are immediately forfeited to the house. After a bust or a stand, play proceeds to the next hand clockwise around the table. When the last hand has finished being played, the dealer reveals the hole card, and stands or draws further cards according to the rules of the game for dealer drawing. When the outcome of the dealer’s hand is established, any hands with bets remaining on the table are resolved (usually in counter-clockwise order): bets on losing hands are forfeited, the bet on a push is left on the table, 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 and is treated independently of the main wager. It pays 2:1 (meaning that the player receives two dollars for every dollar bet) and is 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 blackjack and disappointment for the player. It is attractive (although not necessarily wise) for the player to insure against the possibility of a dealer blackjack by making a maximum “insurance” bet, in which case the “insurance proceeds” will make up for the concomitant loss on the original bet. The player may add up to half the value of their original bet to the insurance and these extra chips are placed on a portion of the table usually marked “Insurance pays 2 to 1”.

Players with a blackjack may also take insurance, and in taking maximum insurance they commit themselves to winning an amount exactly equal to their main wager, regardless of the dealer’s outcome. Fully insuring a blackjack against blackjack is thus referred to as “taking even money”, and paid out immediately, before the dealer’s hand is resolved; the players do not need to place more chips for the insurance wager.

Insurance bets are expected to lose money in the long run, because the dealer is likely to have blackjack less than one-third of the time. However the insurance outcome is strongly anti-correlated with that of the main wager, and if the player’s priority is to reduce variation, they might choose to pay for this.

Furthermore, the insurance bet is susceptible to advantage play. It is advantageous to make an insurance bet whenever the hole card has more than a chance of one in three of being a ten. Advantage play techniques can sometimes identify such situations. In a multi-hand, face-up, single deck game, it is possible to establish whether insurance is a good bet simply by observing the other cards on the table after the deal; even if there are just 2 player hands exposed, and neither of their two initial cards is a ten, then 16 in 47 of the remaining cards are tens, which is larger than 1 in 3, so insurance is a profitable bet. This is an elementary example of the family of advantage play techniques known as card counting.

Bets to insure against blackjack are slightly less likely to be advantageous than insurance bets in general, since the ten in the player’s blackjack makes it less likely that the dealer has blackjack too.

Rule variations and effects on house edge

Doubling down. The third card is placed at right angles to signify that the player cannot receive any more cards.

The rules of casino blackjack are generally determined by law or regulation, which establishes certain rule variations allowed at the discretion of the casino. The rules of any particular game 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 edge”, a statistical advantage for the casino that is built into the game. The advantage of the dealer’s position in blackjack relative to the player comes from the fact that if the player busts, the player loses, regardless of whether the dealer subsequently busts. Nonetheless, blackjack players using basic strategy will lose less than 1% of their 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 generally expected to be greater.

  • Dealer hits soft 17

A “soft 17” in blackjack. An ace and any combination of 6.

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 players draws a ten on their 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 or discourage play altogether. When offering single deck blackjack games, casinos are more likely to disallow doubling on soft hands or after splitting, to restrict resplitting, require higher minimum bets, 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.
Number of decks House advantage
Single deck 0.17%
Double deck 0.46%
Four decks 0.60%
Six decks 0.64%
Eight decks 0.65%
Late/early surrender

Surrender, for those games that allow it, is usually not permitted against a dealer blackjack; if the dealer’s first card is an ace or ten, the hole card is checked to make sure there is no blackjack before surrender is offered. This rule protocol is consequently known as “late” surrender. The alternative, “early” surrender, gives player the option to surrender before the dealer checks for blackjack, or in a no-hole-card game. Early surrender is much more favorable to the player than late surrender. Most medium-strength hands should be surrendered against a dealer Ace if the hole card has not been checked.

For late surrender, however, while it is tempting to 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 one in four 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 cards of a post-split hand have the same value, most games allow the player to split again, 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”).
Hit/resplit split aces
After splitting aces, the 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. Games allowing aces to be resplit are not uncommon, but those allowing the player to hit split aces are extremely rare. 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%. Note that a ten-value card dealt on a split ace (or vice versa) is a “soft 21” and not a “natural”.
No double after split
After a split, most games allow doubling down on the new two-card hands. Disallowing doubling after a split increases the house edge by about 0.12%.
Double on 9/10/11 or 10/11 only
Under the “Reno rule”, double down is only permitted on hard totals of 9, 10, or 11 (under a similar European rule, only 10 or 11). Basic strategy would otherwise call for some doubling down with hard 9 and soft 13–18, and advanced players can identify situations where doubling on soft 19–20 and hard 8, 7 and even 6 is advantageous. The Reno rule prevents the player from taking advantage of double down in these situations and thereby increases the player’s expected loss. The Reno rule increases the house edge by around 1 in 1,000, and its European version by around 1 in 500.
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 or her 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 aces against a dealer 10, where it is still correct to split. In all other cases, a stand, hit or surrender is called for. 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 a winning blackjack
In many casinos, a blackjack pays only 6:5 or even 1:1 instead of the usual 3:2. This is most common at tables with lower table minimums. Although this payoff was originally limited to single-deck games, it has spread to double-deck and shoe games. 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 blackjack machines generally pay 1:1 payout for a blackjack.
Dealer wins ties
The rule that bets on tied hands are lost rather than pushed is catastrophic to the player. Though rarely used in standard blackjack, it is sometimes seen in “blackjack-like” games such as in some charity casinos.