Blackjack Card Counting – How It Works

Most people have the wrong idea about card counting, mainly because they lack an understanding of its mechanics. They assume one needs to be a savant or a mathematical genius to count cards. This misconception results from the way card counting is depicted in media and Hollywood productions like Rain Man, 21, and The Bachelor, among others.

And indeed, who can forget the epic scene in Rain Man where the autistic character of Dustin Hoffman counts cards at a six-deck blackjack table in Caesars Palace and helps his brother (portrayed by actor Tom Cruise) amass a small fortune? As impressive as this scene is, it grossly exaggerates the qualities needed to count cards.

You do not necessarily have to be an autistic savant or have a photographic memory to learn this advantage play technique. This is not to say card counting is easy as pie, though. It requires a good amount of practice, but most people can master it if they invest enough time, efforts, and understanding. This article introduces you to the foundations of this technique and offers a few explanations of how it works.

What is Card Counting and Why Does it Work?

Card CountingBlackjack is different from all other games on the casino floor because it is based on dependent trials. What this means is the past affects the probability of what is going to happen in the future.

Suppose you take a standard deck containing 52 cards and start pulling cards out at random. You pick an Ace, set it aside, and draw again. What are the chances of you pulling another Ace on your next try? They have now decreased because you have only three Aces left after the first draw. If you remove all Aces from the deck on the next draws, the probability of pulling this card would be zero.

The point of this example was to show you the odds in blackjack fluctuate with each card that leaves the deck. The odds of you winning a given hand depend on the cards that have been removed from the deck(s) during the previous rounds and this is precisely what makes the game exploitable.

Some cards favor the dealer. Their removal from the deck increases your chances of winning and has a positive effect on your expected value. Other cards favor the player so the odds of the player beating the dealer decrease proportionally to their removal.

Blackjack Card Counting Gameplay


The Foundations of Card Counting

blackjack countingBefore we proceed further, we would like to warn you that it is impossible to count cards effectively without learning perfect basic strategy first. This is the first step toward becoming a successful card counter and blackjack player in general.

Once you are perfect at basic strategy, you can proceed to learn a card counting system. Most professional blackjack players prefer to use the popular Hi-Lo system because it is simpler to learn but still very effective. You can read about the value this system assigns to the cards below.

The Values of the Cards

blackjack 21After the dealer reshuffles the deck or shoe, the number of high and low cards is equal. The composition of the deck or shoe changes as the game progresses. Card counters track the cards that are dealt during the previous rounds, which gives them knowledge about the composition of the undealt cards.

They assign a value to each card that leaves the deck or shoe. High cards (Ace, 10, King, Jack, and Queen) are favorable for the player so they are assigned a count value of -1. When the deck or shoe is depleted from these high cards, the edge of the player also decreases.

The low cards (2, 3, 4, 5, and 6) are favorable for the dealer. They are assigned a count value of +1 because when dealt, there are fewer of them left to hurt the player. The cards with denominations of 7, 8 and 9 are considered neutral and have a value of 0 because the effect of their removal on the player’s expected value is much less pronounced.

Converting Running Count into True Count

blackjack card countingWhat a card counter does is add up the values of every card that appears on the layout. The sum total of these cards gives them what is known as the running count (RC). For instance, suppose you are dealt a starting hand that consists of 4-5 and then you draw a King. This gives you a running count of +1. At the end of each round of play, you arrive at a positive, negative or zero running count.

When the running count is positive, this means more low cards have been dealt during the previous round. Respectively, the deck or shoe now contains more high cards than low cards which is favorable for the player.

If the running count is negative, more high cards have been dealt. The deck now favors the house because more low cards remain to be dealt. When the running count is zero, the number of high and low cards that remain to be played is equal. The deck is now neutral as it was immediately after the shuffle.

It is worth mentioning that card counters win fewer hands than they lose but still generate more profits than losses. This is possible because they increase the size of their bets during positive counts when they have the advantage and decrease it during negative counts when the edge swings over to the house.

Deck Estimation

Deck EstimationEstimating how many decks remain to be dealt is obviously a necessity when you count cards. This is something that requires a good amount of practice. There are several ways to approach deck estimation. Some players prefer to take a look at the shoe but this method is not as accurate because sometimes the cards are not packed tightly and not all of them are clearly visible.

It is more common for card counters to use the discard tray for guidance and subtract the number of decks there from the number of decks the shoe started with. While more accurate than looking at the shoe, this method is also not optimal because it does not take into account the cards on the layout. Additionally, staring at the discard tray helps the pit crew detect counters. Some casinos even take measures by hiding the discards in the tray.

Some single-deck players take notice of how many hands have been played, then multiply the result by 2.7 and subtract from the overall number of cards. But the most accurate method to estimate how many decks have been played is by subtracting the cards you have seen, which includes both the cards you see on the layout and those in the discard tray. Whichever method you choose, make sure you practice it at home until you can determine the number of decks that remain with absolute precision.

Using a Bet Spread

Bet SpreadAs was said, card counting gives you an edge because you adjust your bets’ size in accordance with the count and bet more when you have an advantage. Two of the most common mistakes aspiring card counters commit are over-betting and under-betting their bankroll.

When over-betting, you pour more money into a hand than you should because you overestimate your advantage. This exposes you to a higher risk of ruin and you stand good chances of blowing your entire bankroll away.

Under-betting is basically the opposite but it is just as detrimental for the player. Some people bet less than they should because they are afraid of detection. Others do it because they are too scared they might end up losing their large bets. The trouble is if you do not bet enough money when you have the advantage, you are playing a break-even game at best.

Using Indices

blackjack indicesWe mentioned earlier learning perfect basic strategy is an absolute necessity if you want to be a successful card counter. By keeping track of the cards that are dealt, card counters know when it is the right time to deviate from basic strategy. These deviations from basic strategy are called indices.

You need to deviate because some basic strategy plays are no longer optimal when the composition of the remaining deck or shoe changes. Do not forget that basic strategy relies on limited information and takes into account only your hand total against the dealer’s upcard.

Just to give you an example of what we mean, basic strategy tells you to never take insurance. What’s interesting, though, is that insurance actually becomes a good bet during high positive counts of +3 and above. The shoe or deck is rich in high cards on such positive counts which increases the chances of the dealer having a blackjack. Another example is the play for a hard 15 against a dealer’s 10. The index number here is +4, which means you should stand instead of hitting but only on positive counts of +4 or above.

Some professional blackjack players succeed in memorizing a hundred or more indices. This is indeed impressive but if you are new to card counting, we recommend you to start with the Illustrious 18 and the Fabulous 4. Blackjack authority Donald Schlesinger outlines them as the most important indices in his book Blackjack Attack. You can learn more about those index numbers in the article about the Hi-Lo system.


blackjack back-countingThere are two main betting strategies card counters can use. The first approach is to play the entire shoe from start to finish where you adjust your bets on negative and positive counts as the true count dictates. For some players, this is the only possible approach because certain gambling establishments prohibit them from entering games in progress. This is known as the “No Mid-Shoe Entry” rule.

Back-counting allows players to further increase their expected value because they place their bets on positive counts only when they have the advantage. This approach is also known as wonging in and out of a game. You wong in, i.e. join a table, when the true count is greater than zero, typically when it reaches or exceeds +2. You wong out, or quit playing, when the true count drops below zero. Many players choose to wong out on true counts of -1.

When choosing an approach, your decision should be based on factors like the playing conditions and the size of your bankroll. At some casinos, joining a table in the middle of the shoe is not allowed. On the other hand, if you are just starting to build a blackjack bankroll, you might want to try back-counting because it decreases variance and causes you to play fewer rounds per hour.

Some players are reluctant to back-count because this attracts the attention of the pit crew and exposes them to a higher risk of detection. Card counting is not illegal, but casinos are private properties and as such, have the right to prohibit card counters from playing on their premises.

Card Counting in the Actual Casino Environment

blackjack card countingA player is not required to be a rocket scientist or a math genius to count cards, but the harsh reality is that counting in the comfort of your home is much easier than doing it in an actual landbased casino. Things can get pretty hectic at the blackjack tables which causes many rookies to lose their count and make costly mistakes.

If you want to be a successful advantage player, you need to be able to overcome these distractions. You can try practicing at home with the help of some of your close friends. Try listening to music at a high volume while your friends “distract” you the same way other players and cocktail waitresses do in the actual casino.

It is just as important to master the ability to avoid detection. You will not be able to generate any expected value if you are barred from all casinos in your area. When you find a good game with great conditions, you need to cherish it and make longevity your priority. Some professional players use cover to prevent the casino personnel from identifying them as counters.

Cover comes in many different shapes and forms, including unorthodox plays, betting big during negative true counts (this takes away from your EV, though), pretending to be a clueless or inebriated player, and even physically disguising yourself. One male member of the MIT team, for example, went as far as dressing up as a female Asian player and succeeded to avoid detection for a while.