How to count cards in blackjack: the method and its limits

Counting cards in blackjack has nothing to do with magic tricks or a photographic memory. You keep a single number up to date as the cards come out, to know whether the ones still in the shoe favour the player or the house. The technique is real, documented since the 1960s, and it works under precise conditions.

Those conditions are exactly what most guides leave out. So it is worth looking at how the method works, what a player really gets from it, and why it collapses the moment the game moves online.

Card counting in one simple idea

Blackjack is dealt from a shoe of several decks, which every round eats into a little further until the next shuffle. As long as it is not reshuffled, each card dealt changes the make-up of those left behind. After a run of small cards, proportionally more tens, picture cards and aces remain; after a run of high cards, the opposite is true.

A counter is therefore not trying to guess the next card. They measure a trend: the share of high cards still to come. When that share rises, the next hand becomes slightly more favourable to the player than usual, and that is all counting can tell you.

Why a shoe full of high cards helps the player

High cards work in the player's favour for three reasons. They produce more natural blackjacks, and even if the dealer gets as many as you, only yours is paid at 3 to 2. They make doubling down more profitable, since a 10 or 11 is more likely to catch a picture card. And the dealer has no choice: they must draw on 16 or less, and a shoe loaded with high cards makes them go over 21 more often.

The reverse also holds. A shoe short on picture cards helps the house: small cards let the dealer complete middling hands without going bust, and your doubles more often end on a poor total.

Counting cards with the Hi-Lo system

The most widely used method is called Hi-Lo. Harvey Dubner published it in 1963, a year after the book in which Edward Thorp proved, figures in hand, that blackjack could be beaten. Each card gets a value:

• the small cards, from 2 to 6, add 1 to the total;
• the 7, 8 and 9 stay neutral;
• every 10, picture card or ace takes 1 away.

You start at zero after the shuffle, then add the value of every card visible on the table, other players' cards included. A full deck adds up to zero, which doubles as a check. The higher the total climbs, the more small cards have gone, and the richer the rest of the shoe is in high cards. A negative total signals the opposite.

From running count to true count

That total is called the running count. On its own it is not enough, because the same +6 does not carry the same weight with one deck left in the shoe as with five. So you divide it by the number of decks remaining to get the true count.

Take a six-deck shoe. After roughly three decks have been dealt, the running count reaches +6. About three decks remain, so the true count is +2. Later in the same shoe, a running count of +6 with a single deck left gives a true count of +6: the situation is far more favourable, even though the number you started from has not changed.

The true count is what drives decisions. It also means estimating by eye how many decks are left in the shoe, which is part of the learning curve.

What a counter does with the information

Counting does not replace basic strategy, it builds on it. A counter first plays every hand according to the basic strategy for blackjack, then draws on two levers. The first is the bet: small when the true count is neutral or negative, larger as it rises. The second is departing from the chart in a few specific situations where the make-up of the shoe changes the best decision.

Insurance is the best-known example. Normally a poor bet, with Hi-Lo it becomes profitable from a true count of +3, because there are then enough ten-value cards left in the shoe.

The gain stays modest. Wizard of Odds ran the numbers: a counter playing a six-deck shoe, with five decks dealt before the shuffle, at a table with favourable rules, betting from 1 to 15 units and using every chart deviation, ends up with an edge of about 1.18%. A real but thin advantage, which only shows after thousands of hands and with sharp ups and downs between sessions.

From Thorp to the MIT students

Counting was born with Beat the Dealer, published by Edward Thorp in 1962: the mathematician showed, with computer simulations, that a player who tracks the make-up of the shoe can turn the house edge around. Casinos reacted quickly, adding more decks and shuffling earlier.

The technique then became a team sport. In the 1980s and 1990s, MIT students organised themselves into groups where some counted at small stakes while others came in to bet big once the table turned favourable. Their story, brought to the screen in 21, mostly fed the legend of card counting.

The countermeasures are well known: a shoe of six or eight decks, a cut card placed well before the end, continuous shuffling machines that make the count useless, and the option of limiting the stakes of a player who has been spotted.

Counting cards in online blackjack: why the count keeps resetting

Counting rests on a single condition: a shoe that runs down without being reshuffled. Yet most online blackjack tables start from a full set of cards on every hand. First Person Blackjack from Evolution, for example, uses a eight-deck shoe that is completely renewed every round. The cards from the previous hand then have no influence on the next one, and the count drops back to zero before it has even started.

Among the casino live games, each blackjack table has its own rules, which you can open from within the game. They state how the shoe is shuffled, and therefore whether tracking the cards makes any sense at all.

What stays useful online is what counting already assumes: playing every hand by basic strategy, knowing the table rules and keeping a stake that suits your budget. If you want to play blackjack online on that basis, each game's return to player is shown in its information panel.

Is card counting allowed?

Counting in your head uses no hidden information: the player works with cards laid face up in front of everyone. That is why mental counting is not treated as cheating in the jurisdictions that have settled the question. The line is drawn at devices: in Nevada, using a device to calculate your odds at a casino table is a felony.

Allowed does not mean welcome. A Nevada casino can refuse a counter's bets or ask them to leave the table. New Jersey took a different route: in 1982 its Supreme Court ruled that an Atlantic City casino could not exclude Ken Uston on that ground alone, since setting the rules of the game falls to the state's casino control commission.

In online blackjack the question barely arises: with a fresh shoe on every hand, there is simply nothing to count. What frames your game instead are Belgium's online gambling rules: you must be 21 or over, hold a verified account and stay within a weekly deposit limit.

At Crazy Dice, you play on the Belgian-licensed online casino B+19490, and your decisions and your budget remain the only levers. Open a Crazy Dice account and put basic strategy to work with real stakes.

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