Rules

Blackjack hands are scored by their point total. The hand with the highest total wins as long as it doesn't go over 21, which is called a bust. Cards 2 through 10 are worth their face value, and face cards (jack, queen, king) are also worth 10. An ace counts as 11 unless it would bust a hand, in which case it counts as 1.

The goal of each player is to beat the dealer, by having the higher, unbusted hand. Note that if the player busts he loses, even if the dealer also busts. If the player's and the dealer's hands have the same point value, this is known as a "push", and neither player nor dealer wins the hand.

After initial bets are placed, the dealer deals the cards, either from one or two hand-held decks of cards, known as a "pitch" game, or more commonly from a shoe containing four or more decks. The dealer gives two cards to each player, including himself. One of the dealer's two cards is face-up so all the players can see it, and the other is face down. (The face-down 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 are dealt face up from a shoe, or face down if it is a pitch game.

A two-card hand of 21 (an ace plus a ten-value card) is called a "blackjack" or a "natural", and is an automatic winner. A player with a natural is usually paid 3:2 on his bet, although in 2008 some casinos started paying only 6:5 on blackjacks, a move decried by longtime blackjack players.

This is the summary of how the play proceeds after the deal.

• If the dealer has a blackjack and the player doesn't, the dealer wins automatically.
• If the player has a blackjack and the dealer doesn't, the player wins automatically.
• If the player and dealer both have blackjack, it's a tie (push).
• If neither side has a blackjack, then the first player completely plays out his hand, followed by the next player, and so on.
• When all the players have finished the dealer plays his hand.

The player's options for playing his hand are:

• Hit (take another card)
• Stand (take no more cards)
• Double down (double the wager, take exactly one more card, and then stand)
• Split (when the player has identical value cards, such as 8,8, place an additional wager and have each card be the first card in a new hand)
• Surrender (forfeit half his bet and give up his hand. Surrender is not offered at most casinos.)

The player's turn is over after any of the following happens:

• He decides to stand.
• He busts. (in which case he loses even if the dealer subsequently busts, this is the source of the house advantage)
• He doubles down and receives exactly one more card.

After all the players have finished making their decisions, the dealer then reveals the hidden hole card and plays his hand. House rules say that the dealer must hit until he has at least 17, regardless of what the players have. In most casinos a dealer must also hit a soft 17 (such as an Ace and a 6). The table felt will indicate whether the dealer hits or stands on soft 17.

If the dealer busts then all remaining players win. Bets are normally paid out at the odds of 1:1.

Some common rules variations

• one card split aces: one card is dealt on each ace, players turn is over.
• early surrender: player has the option to surrender before dealer checks for BlackJack.
• late surrender: player has the option to surrender after dealer checks for BlackJack.
• double-down restrictions: double-down allowed only on certain combinations.

Insurance

If the dealer's upcard is an Ace, the players are offered the option of insurance before the dealer views the 'hole card'. This is a side-bet that pays back 2:1 if the dealer has a "natural". The insurance wager is exactly half the amount of the player's original bet. Insurance is considered a bad bet because it carries a high house edge (casino profit).

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 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 skilled player:

1. Doubles are permitted on any two-card hand except 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. Normal (aka "late") surrender.
5. Resplitting Aces.
6. Drawing more than one card against a split Ace.
7. Five or more cards with the total still no more than 21 as an automatic win

The following rules are detrimental to the skilled 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 (to 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

The above is a basic strategy table for the most common 6- to 8-deck, Las Vegas Strip rules. Specifically: dealer hits on soft 17, double after split allowed, multiple split aces, one card to split aces, blackjack pays 3:2, and (optionally) late surrender.

Key:

S = Stand

H = Hit

D = Double

SP = SPlit

R = suRrender if allowed, otherwise hit

Rs = suRrender if allowed, otherwise Stand

Rsp = suRrender if allowed, otherwise SPlit

In some LV Strip casinos you may still be able to find the older version of the multi-deck shoe game, where dealer stands on soft 17; those are usually high minimum ($50 or more) tables. This version is much more advantageous to the player, but requires a slightly modified basic strategy table.

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 of certain events occurring on the next deal. In proper statistics terms, this is known as the Law of Independent Trials - past events have no effect on future probabilities. 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 wins only even money, while the player is paid 3:2). When the deck has more small cards such as 4s, 5s, and 6s, it is more likely that the player will be dealt a bad hand and bust, favoring the dealer (likewise, it increases the chance of a dealer busting 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 remaining 10 count cards and Aces to offer a positive expectation 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 more often than 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 such as 4s and 5s, and rich in 10s, that may alter the odds in favor of standing.

It is difficult for most people to remember what cards have already been dealt, particularly from a multiple deck shoe. Therefore, most card counting schemes assign a positive, negative, or zero point value to 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 negative value. The exact number assigned to the cards depends on the specific card-counting method. The card counter mentally keeps a running tally of the point values as they are dealt. 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). Highly skilled counters have an expectation of 1 to 1.6% gain; and number perhaps a few hundred. It is probably safe to say that the best counters earn in the very low six figures of US dollars, comparable with those in other mentally exacting fields. Other counters may use counting on occasional vacations, allowing the vacation to more than pay for itself (especially since, like other big players, they are often comped heavily by casinos).

If the tally is 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, to avoid facing casino countermeasures. In practice, the vast majority of people who attempt to count cards lose money through errors; casinos who notice a counter will often check to see if the counter is good enough to have a positive expectation, and ignore them otherwise. This detection process is mistake-prone.

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; this bet is in general almost always disadvantageous.

Counting schemes that 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. While playing out hands, Aces are slightly disadvantageous for the player, which implies that they should have a positive point count; but for purposes of getting a blackjack, they are extremely valuable when they remain in the deck. Most counting schemes give aces a negative count, recognizing that there is a compromise involved in this process. Some schemes actually assign a zero value to aces, and require the counter to keep a separate side count of aces.

The theory of card-counting, and the first counting scheme, was published in 1962 by American mathematician Edward O. Thorp in his book Beat the Dealer, which is now regarded as a classic in the gambling literature genre. Much of the specific detail in the work, however, is no longer up-to-date— end play, for example, has practically disappeared because the casinos no longer deal to the last card, in a (somewhat panicked, some say) response to the book. Also, the counting system described (10-count) is harder to use and less profitable than the point-count systems that have been developed afterwards.

The most commonly used system by most professionals (both players and surveillance) is Hi-Lo. It assigns -1 to 10's and Aces, +1 to 2 through 6. Higher level counts theoretically generate higher profits, but for most players, decreased playing speed and increased fatigue and error rates argue against their use. K-O, an unbalanced count (7's are also +1) developed by Ken Fuchs and Olaf Vancura (Knock Out Blackjack), is only modestly less effective than Hi-Lo, but is substantially less error-prone.

In the early days of card-counting, it is undoubted that a few players were hugely successful. Ken Uston recounts his early successes—and court battles with the casinos—in his book Ken Uston on Blackjack. In reality, Ken Uston, though perhaps the most famous card counter through his 60 Minutes television appearance and his books, was overall only a small winner. The most financially successful card counters have made their fortunes in other businesses. Ed Thorp, for example, runs a successful fund.

There have been several MIT Blackjack Teams, made up of MIT students who team up to use a combination of card counting and group play to attempt to beat the house.

The most successful independent team is the one founded by Thomas Hyland in 1979. Dubbed by some as the "King of Card Counting," Hyland personally trained the members to work individually and later in teams to win millions at Atlantic City, Las Vegas, Caribbean and Canadian casinos. When the casinos caught on to them, Hyland developed the "ace locating" technique. This made it more difficult for casinos to detect when the players were card counting. In 1994, members of the team were arrested for card counting at Casino Windsor in Ontario, Canada. However, the judge ruled that the players' conduct was not cheating, but merely the use of stategy as it did not physically alter the game.

Casino counter-measures

Casinos can counter card counting by using large quantities of decks in dealing cards. "Shoes" consisting of 6 or 8 decks are common. Increasing the number of decks decreases the tendency of the count to vary widely, offering the card counter fewer opportunities to take advantage of a player-advantageous count.

Player advantage can also be decreased by more frequently shuffling the cards. The shallower the "penetration" (the proportion of the shoe consumed before reshuffling), the less opportunity there is for the count to vary.

However, for the casinos there is a downside to frequent shuffling: It reduces the amount of time that the noncounting players are playing and consequently losing money to the house. It has become common for casinos to use automatic shuffling machines to compensate for this. Some models of shuffling machines shuffle one set of cards while another is in play. Others, known as Continuous Shuffle Machines (CSMs) allow the dealer to simply return used cards to a single shoe to allow playing with no interruption. Because CSMs essentially force minimal penetration, they remove almost all possible advantage of traditional counting techniques. As a result, some blackjack players call for a boycott of tables using CSMs.

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 loud, distracting environments of most casinos, and even the availability of complimentary alcoholic beverages, play roles as casino counter-measures.

Casinos also look out for known card counters, who may be banned from play depending on regulatory commission rules. They also look for suspicious actions such as a long series of small bets followed by large one. Monitoring player behavior to assist in this identification falls to on-floor casino personnel ("pit bosses") and central security personnel who may use video surveillance ("the eye in the sky") as well as computer analysis to try to spot playing behavior indicative of card counting; early counter-strategies featured the dealer learning to count the cards themselves to recognise the patterns in the players. In addition, many casinos employ the services of various agencies who claim to have a catalog of advantage players. If a player is found to be in the Griffin Book or Biometrica, he will almost certainly be stopped from play and asked to leave regardless of his table play. For successful card counters, therefore, skill at "cover" behavior to hide counting to avoid "drawing heat" and possibly being barred, may be just as important as playing skill.

Casinos 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.

There have been some high-profile lawsuits involving whether 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, as working figures within one's own mind is not an arrestable offence. Using an outside aid, though, is illegal. However, the casinos despise counters and, if permitted by their jurisdiction, may ban counters from their casinos; 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 a player for life. Some skilled counters try to disguise their identities and playing habits; however, some casinos have claimed that facial recognition software can often match a camouflaged face with a banned one. Whether this is true is unknown.

Most casinos now hire consulting firms to help them track card counters.

Finally, the simplest countermeasure the casinos use in order to thwart card counting is simply to offer an inferior blackjack payoff of 6:5 instead of the standard 3:2. 6:5 blackjack is over eight times worse mathematically for the player than in a typical game with a regular payoff, expert player and novice alike cannot beat the game as a practical matter. The casinos offer this game using a single deck, which attracts players who think this gives them an advantage, when in fact the benefit of a single deck is outweighed several times over by the short blackjack payoff.

Modern technology is also providing some advantage in monitoring for card counters, for example the MindPlay system.

Variants

Many casino games are based off the ideas in blackjack. Spanish 21 provides players with many liberal blackjack rules, such as doubling down any number of cards (with the option to 'rescue', or surrender only one wager to the house), payout bonuses for five or more card 21's, 6-7-8 21's, 7-7-7 21's, late surrender, and player blackjacks always winning and player 21's always winning, at the cost of having no 10 cards in the deck (though there are jacks, queens, and kings). With correct basic strategy, a Spanish 21 game has a lower house edge than a comparable blackjack game.

Certain rules changes are employed to create new variant games. These changes, while attracting the novice player, actually increase the house edge in these games. Double Exposure Blackjack is a variant in which the dealer's cards are both face-up. This game increases house edge by paying even-money on blackjacks and players losing ties. Double Attack Blackjack has very liberal blackjack rules and the option of increasing one's wager after seeing the dealer's up card. This game is dealt from a Spanish shoe, and blackjacks only pay even money.