Blackjack, also known as twenty-one, is the most widely played casino banking game in the world. Blackjack is a comparing card game between a player and dealer, meaning that players compete against the dealer but not against any other players. Blackjack is played with one or more decks of 52 cards. The object of the game is to reach 21 points or to reach a score higher than the dealer without exceeding 21.
The player or players are dealt an initial two card hand and add the total of their cards. Face cards (Kings, Queens, and Jacks) are counted as ten points. The player and dealer can count his own ace as 1-point or 11 points. All other cards are counted as the numeric value shown on the card. After receiving their initial two cards, players have the option of getting a “hit,” which means taking an additional card. In a given round, the player or the dealer wins by having a score of 21 or by having the highest score that is less than 21. Scoring higher than 21 (called “busting” or “going bust”) results in a loss. A player may win by having any final score equal to, or less than 21 if the dealer busts. If a player holds an ace valued as 11, the hand is called “soft”, meaning that the player cannot go bust by taking an additional card; otherwise, the hand is “hard”.
The dealer has to take hits until his cards total 17 or more points. (In some casinos, the dealer also hits on a “soft” 17, e.g. initial ace and six.) Players who do not bust and have a total higher than the dealer, win. The dealer will lose if he or she busts, or has a lesser hand than the player who has not busted. If the player and dealer have the same point total, this is called a “push” and the player typically does not win or lose money on that hand.
Many rule variations of blackjack exist. 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 wager and playing strategies accordingly.
Other casino games inspired by blackjack include Spanish 21 and pontoon. The recreational British card game of black jack is a shedding-type game and unrelated to the subject of this article.
Rules of Play At Casinos
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 place their bets 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; 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.
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 receives its second card face down immediately (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 which are 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 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 creating card totals which will turn out to be higher than the dealer’s hand, but without exceeding 21 (“busting”/”breaking”). 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 nor 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. In the case of a tied score, known as “push” or “standoff”, bets are normally returned without adjustment; however, a blackjack beats any hand which is not a blackjack, even with value 21. Blackjack vs. blackjack is a push. Wins are paid out at 1:1, or equal to the wager, except for winning 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.
Blackjack games almost always provide a side bet called insurance, which may be played when dealer’s upcard is an ace. At least one further side bet is usually provided.
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: (handheld) Scrape cards against table. (face up) Tap the table or wave hand toward body.
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: 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 (only available as first decision of a hand): If the first two cards 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 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. 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 T-T may be split, but not of T-K. However, usually all ten-value cards are treated the same. Doubling and further splitting of post-split hands may be restricted, and blackjacks after a split are counted as non-blackjack 21 when comparing against the dealer’s hand. 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”, usually in hole card games and directly after the dealer has checked for blackjack (but see below for variations). When the player surrenders, the house takes 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 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. Note: a “soft” hand is one including an ace counted as 11; other hands are “hard”. 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 counterclockwise order): bets on losing hands are forfeited, the bet on a push is left on the table, and winners are paid out.
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 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, it is reasonable 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 good 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 Their Consequences For The House Edge
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 which 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 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 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.
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 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.
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 one in 1000, and its European version by around two in 1000.
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 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. 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 usually at tables with the lowest table minimums and single-deck 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. 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. Though rarely used in standard blackjack, it is sometimes seen in “blackjack-like” games such as in some charity casinos.
Each blackjack game has a basic strategy, which is playing a hand of any total value against any dealers upcard which loses least money to the house in the long term.
The bulk of basic strategy is common to all blackjack games, with most rule variations calling for changes in only a few situations. For example, if the above game used the hit soft 17 rule, common in Las Vegas Strip casinos, only 5 cells of the table would need to be changed: double on 11 vs. A, surrender 15 or 17 vs. A, double on A,7 vs. 2, double on A,8 vs. 6. Also when playing basic strategy never take insurance or “even money.”
Estimates of the house edge for blackjack games quoted by casinos and gaming regulators are generally based on the assumption that the players follow basic strategy and do not systematically change their bet size. Most blackjack games have a house edge of between 0.5% and 1%, placing blackjack among the cheapest casino table games. Casino promotions such as complimentary matchplay vouchers or 2:1 blackjack payouts allow the player to acquire an advantage without deviating from basic strategy.
Basic strategy is based upon a player’s point total and the dealer’s visible card. Players may be able to improve on this decision by considering the precise composition of their hand, not just the point total. For example, players should ordinarily stand when holding 12 against a dealer 4. However, in a single deck game, players should hit if their 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 10s 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, even when basic and composition-dependent strategy lead to different actions, the difference in expected reward is small, and it becomes even smaller with more decks. Using a composition-dependent strategy rather than basic strategy in a single deck game reduces the house edge by 4 in 10,000, which falls to 3 in 100,000 for a six-deck game.
Many blackjack tables offer a side bet on various outcomes including:
Player hand and dealer’s up card sum to 19, 20, or 21 (“Lucky Lucky”)
Player initial hand is a pair (“Perfect pairs”)
Player initial hand is suited, suited and connected, or a suited K-Q (“Royal match”)
Player initial hand plus dealer’s card makes a flush, straight, or three-of-a-kind poker hand (“21+3”)
Player initial hand totals 20 (“Lucky Ladies”)
Dealer upcard is in between the value of the players two cards (“In Bet”)
First card drawn to the dealer will result in a dealer bust (“Bust It!”)
One or both of the players cards is the same as the dealers card (“Match the Dealer”)
Player allowed to make optional second hand, and effectively receive the hand of 10,8, or 18 without drawings cards (“Instant 18”)
The side wager is typically placed in a designated area next to the box for the main wager. A player wishing to wager on a side bet is usually required to place a wager on blackjack. Some games require that the blackjack wager should equal or exceed any side bet wager. A non-controlling player of a blackjack hand is usually permitted to place a side bet regardless of whether the controlling player does so.