Editing Blackjack (section)

====Card counting====
{{Main|Card counting}}

During the course of a blackjack shoe, the dealer exposes the dealt cards. Players can infer from their accounting of the exposed cards which cards remain. These inferences can be used in the following ways:
* Players can make larger bets when they have an advantage. For example, the players can increase the starting bet if many aces and tens are left in the deck, in the hope of hitting a blackjack.
* Players can deviate from basic strategy according to the composition of their undealt cards. For example, with many tens left in the deck, players might double down in more situations since there is a better chance of getting a good hand.

A card counting system assigns a point score to each card rank (e.g., 1 point for 2–6, 0 points for 7–9, and −1 point for 10–A). When a card is exposed, a counter adds the score of that card to a running total, the 'count'. A card counter uses this count to make betting and playing decisions. The count starts at 0 for a freshly shuffled deck for "balanced" counting systems. Unbalanced counts are often started at a value that depends on the number of decks used in the game.

Blackjack's house edge is usually around 0.5–1% when players use basic strategy.<ref>{{Cite web |title=Blackjack - Beating Bonuses |url=http://www.beatingbonuses.com/blackjack.htm#table |website=beatingbonuses.com}}</ref> Card counting can give the player an edge of up to about 2%.<ref name="TOB">{{Cite book |last=Griffin |first=Peter |title=The theory of blackjack: the compleat card counter's guide to the casino game of 21 |date=March 1, 1999 |publisher=Huntington Press |isbn=978-0929712130 |edition=6th}}</ref>{{rp|5}}

Card counting works best when a few cards remain. This makes single-deck games better for counters. 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, casinos limit penetration by ending the shoe and reshuffling when one or more decks remain undealt. Casinos also sometimes use a shuffling machine to reintroduce the cards whenever a deck has been played.

Card counting is legal,<ref name="TOB" />{{rp|6–7}} but a casino might inform counters that they are no longer welcome to play blackjack. Sometimes a casino might ban a card counter from the property.<ref>{{Cite book |last=Thorp |first=Edward O. |url=https://www.worldcat.org/oclc/655875 |title=Beat the dealer: a winning strategy for the game of twenty-one: a scientific analysis of the world-wide game known variously as blackjack, twenty-one, vingt-et-un, pontoon, or van-john |date=1966 |publisher=Random House |isbn=0-394-70310-3 |edition=revised |location=New York |pages=132–136 |oclc=655875}}</ref> The use of external devices to assist in card counting is illegal in [[Nevada]].