Card Counting in Blackjack

Card counting in casinos

What is card counting?

Card counting is a technique used by experienced blackjack players to try and help shift the odds in their favour. By counting the cards that have left the dealer’s shoe, players can more accurately predict whether a high or a low-value card is more likely to be dealt next.

The idea of card counting in blackjack is to help players know when the advantage against the dealer moves in their direction. When the count moves in the player’s favour, card counters will increase the size of their bet to hopefully maximise their wins.

Who invented card counting?

The brain behind the concept of card counting techniques was a man named Edward O. Thorp. The so-called ‘grandfather of card counting’ published a book in 1962 titled ‘Beat the Dealer’. Within this book, Thorp discussed a host of strategies and techniques designed to optimise blackjack play.

Despite Thorp’s groundbreaking revelations and advice, in publishing the book, he enabled land-based casinos to develop countermeasures against his strategies. As a result, today, dealers no longer deal to the last card in the deck. Furthermore, Thorp’s original 10-count counting system has been substituted in favour of the point-count systems that others have developed.

Is card counting possible in online casinos?

There is a crucial difference between card counting at a land-based casino and attempting to card count at an online casino: how the cards are dealt and shuffled. At a land-based casino, blackjack dealers will shuffle single or multiple decks of cards into a dealing shoe. The shoe prevents the cards from being tampered with mid-game. The dealer will continue dealing cards for the game until the cut card is dealt and the decks are reshuffled. This makes it possible to keep a running count on the action.

On the other hand, in an online blackjack game, the shuffle prevents players from using card counting techniques in any way, shape or form. Multi-deck online blackjack games are shuffled using random number generators (RNGs) to completely randomise the outcome of every game. Think of these like the continuous shuffling machines (CSMs), which land-based casinos are increasingly using to also combat card counting in blackjack.

Card counting in Blackjack

Card counting basics

Want to learn how card counting in blackjack works?

Blackjack card counting does not require you to memorise or track specific cards. Instead, players must assign a point score to every card that comes out of the deck. They then track the total of these values over time to ascertain the 'running count'.

The running count helps to determine whether there are more high-value cards or low-value cards remaining in the deck. High-value cards are more beneficial to players than low-value cards, as they create the opportunity for the following:

  • A better chance of landing a natural blackjack and thus receiving the bigger blackjack payout
  • Double downs on additional hands to improve your potential profits
  • More chances to split hands, which the dealer cannot do
  • A larger concentration of tens can make it more beneficial to take the insurance bet when the dealer shows an Ace on their up card

If you want to be a good card counter at the blackjack tables, it’s highly recommended that you familiarise yourself with basic blackjack strategy. Most experienced card counters adhere by the basic strategy even while card counting, to maximise their edge over the house.

Speaking of edges, card counting techniques can tip the balance in your favour by between 0.5%-1%. Although this means you are unlikely to get rich quick, your losing streaks are unlikely to be extreme either.

Card counting systems

What is a card counting system?

A card counting system is a defined set of rules that determines how you keep track of the running count of the game and ascertain when the ratio of high cards to low cards is in your favour instead of the dealer’s.

When you are choosing a blackjack card counting system, it’s important to opt for one you are comfortable with. It doesn’t matter whether you choose the simplest or the most complex system. But you'll want to make sure it’s one that you can stick with and suits your abilities at the tables.

Today’s blackjack card counting systems have evolved immensely from the days of Edward O. Thorp’s original system. Below, we’ll take you through ten of the most popular card counting strategies that you could employ at the tables.

Hi-Lo card counting

Arguably the most common card counting strategy in blackjack today, the Hi-Lo system was first developed by a man named Harvey Dubner in the 1960s. It requires you to begin with a running count of zero at the beginning of the deck or shoe. You’ll then assign values to each card that comes out (+1, 0, or -1) to ascertain whether there is an imbalance of high or low-value cards remaining in the deck.

  • Low cards (2-6) = +1 Low-value cards require you to add one to the running count. The higher the running count, the more high-value cards there are remaining in the deck.  
  • Neutral cards (7-9) = 0 Mid-range cards are considered neutral cards in this system. You are not required to add anything to the running count when these are dealt.  
  • High cards (10-A) = -1 High-value cards require you to subtract one from the running count. The lower the running count, the more low-value cards there are remaining in the deck.

When the running count is high, you should bet more to take advantage of the improved probability of landing natural blackjacks and high-value hands. When the running count is low, you should limit the size of your bets to minimise the damage to your bankroll from losing hands with multiple low-value cards.

Hi-Opt I card counting

Devised by Charles Einstein (no relation to Albert!) back in 1968, the Hi-Opt 1 system has since been enhanced by Carl Cooper and Lance Humble to create an effective card counting system for blackjack.

Hi-Opt 1 is similar to the Hi-Lo strategy in that you are required to build a running count during your gameplay. However, Hi-Opt 1 takes the Hi-Lo strategy a little further by helping create something known as a ‘true count’ alongside the running count. A true count is considered by blackjack professionals to be a more accurate assessment of the cards remaining in the dealer’s deck or shoe.

Hi-Opt II card counting

The Hi-Opt II counting system uses Hi-Opt I as the basis of its strategy whilst implementing alternative point values to try and improve the effectiveness and accuracy of your running count at the table. Hi-Opt II is a more complex system than most, including Hi-Opt I, so might not be best suited for beginners to blackjack card counting.

In Hi-Opt II, there is the addition of a +2 and a -2 point value in the count. Naturally, introducing more values to the counting system can make it harder to maintain an accurate count in action. Below is an outline of the new point values in Hi-Opt II:

  • 2-3 = +1
  • 4-5 = +2
  • 6-7 = +1
  • 8-9 = 0
  • 10-K = -2
  • A = 0

Thorp’s Ten-Count System

As we've touched upon above, the very concept of card counting in blackjack was created by a man named Edward O. Thorp, a maths professor and hedge fund manager by day, and author by night. He pioneered the original card counting theory surrounding single-deck blackjack – the ten-count system.

Thorp’s system requires you to begin a mental count of zero at the start of your game. As the cards are dealt, you are then going to assign each card on the table with a value, regardless of whose hand they belong to. The values are as follows:

  • A, 2, 3, 4, 5, 6, 7, 8, 9 = +4
  • 10, J, Q K = -9

Once you’ve mastered adding four and subtracting nine from the count, you know how to get a running count. However, the casinos soon cottoned on to Thorp’s system, which was optimised for single-deck blackjack. So, what did the casinos do? They introduced blackjack tables using multiple decks, rendering the system null and void. 

KO card counting

The Knock Out (KO) card counting system is an unbalanced card counting system. What do we mean by unbalanced? An unbalanced system is one where the point values for all the cards counted does not add up to zero. A balanced system sees the sum of the count values assigned to each card net out to zero.

Unbalanced systems are a good starting point for beginners who find it difficult to convert the running count into a more accurate true count.

The KO card counting system is similar to the Hi-Lo system, with one major exception. In the KO system, the number seven is considered a low card and a +1 rather than a zero (or neutral) card in Hi-Lo:

  • Low cards (2-7) = +1
  • Neutral cards (8-9) = 0
  • High cards (10-A) = -1

Omega II card counting

The Omega II blackjack counting strategy was the brainchild of Bryce Carlson. The system was very popular in the 1990s and is still sometimes used today. It uses a multi-level points value system, with some card counting values at 2 and others at 1:

  • 4, 5, 6 = +2
  • 2, 3, 7 = +1
  • 8, A = 0
  • 9 = -1
  • 10-K = -2

Although the Omega II system is considered one of the most accurate blackjack counting practices, giving players a great chance of calculating their position in the game at any given time, its complexity makes it less suitable for newcomers to basic blackjack strategy and card counting. It’s also an unbalanced system like the KO strategy, so you’ll never be able to fully determine the true count of your game.

The Ace/Five count

Those seeking total simplicity and accessibility in their blackjack counting practice should look no further than the Ace/Five count system.

First and foremost, you’ll need to predefine a minimum and maximum bet size for your game. At the start of your game, the running count will be zero. Whenever a five comes out of the deck, add 1 to your running count. Whenever an Ace is dealt from the deck, subtract 1 from the count.

From there, whenever your running count is higher than or equal to 2, you double your previous bet to your maximum wager. If the running count falls to less than or equal to one, you stick to your minimum wager.

This strategy is thought to be the most effective at beating the plethora of casinos that now offer six and even eight-deck blackjack games.

Red Seven card counting

The Red Seven system is another strategy that’s been simplified to suit beginners to blackjack counting strategy. Devised by Arnold Snyder in the early 1980s, it uses the following card counting values:

  • 2, 3, 4, 5, 6 = +1
  • 7 red = +1
  • 7 black = 0
  • 8-9 = 0
  • 10-A = -1

To begin your count, you’ll need to multiply the number of decks in play by -2. If you’re sat at a six-deck blackjack table, your count will begin from -12. If, over time, your running count reaches a positive figure, you can increase the size of your wager. By multiplying the number of decks from the outset, you are getting a more accurate true count from the word go.

Halves card counting

In terms of complexity, the Wong Halves card counting system is up there with the toughest blackjack counting practices to master. The Halves card counting strategy begins with zero, but the point values differ greatly:

  • 3, 4, 5, 6 = +1
  • 2, 7 = +0.5
  • 8 = 0
  • 9 = -0.5
  • 10-A = -1

This strategy is one of the most complex but most accurate card counting techniques all the same. It offers a 0.99 betting correlation out of 1.00, allowing players to make confident predictions about the outcome of future cards dealt from the deck. However, the addition of more point-based values can make this system harder to keep on top of in a busy, exciting casino setting.

Zen card counting

Another brainchild of Arnold Snyder, the zen counting system is a balanced strategy that relies heavily on the running count:

  • 4, 5, 6 = +2
  • 2, 3, 7 = +1
  • 8-9 = 0
  • A = -1
  • 10-K = -2

Alongside the Halves card counting system, the zen strategy is up there as one of the most accurate card counting techniques. It offers a betting correlation of 0.96 out of 1.00, so players can bet confidently in the future outcomes of the game, providing they can calculate the point values quickly and accurately. Accurately is the operative word here, as this complex system means it’s all too easy to lose your train of thought amidst the buzz of the casino floor. 

How to count cards in blackjack

Want an easy-to-digest four-step guide to counting cards in blackjack? Read on and try your best to use the following steps.

Pick a value for each card (+1, 0, -1)

The success of any card counting strategy in blackjack is to make sure you are clear on the points value assigned to each card. These card counting values need to be ingrained in your memory, making it easy to keep track of the running count – particularly if there are multiple players at your table.

Track the cards and remember their value

Whatever you do, don’t forget the points values you assign to each card. Any miscalculations can totally mess up your running count and may result in you betting big on the next hand in error. Don’t play blackjack with a card counting system until you are 100% familiarised with these blackjack card counting values.

Add the cards’ values to determine the value of the cards in the deck – the running count

Although you don’t need to be Carol Vorderman to count cards at a blackjack table, you do need to be sharp with numbers. The speed of the game means that you’ll have to be adding and subtracting numbers every few seconds to get an accurate running count. It can be mentally draining, particularly if you’re trying hard not to attract attention from the pit bosses!

When to bet more? When to bet less?

Once you are confident and capable of maintaining an accurate running count, you’ll then be able to use this figure to measure the size of your bets at the blackjack tables. A positive count, e.g. +2, means that you should increase the size of your bets, while a negative count, e.g. -2, means that you should rein in the size of your wagers to maximise the lifespan of your bankroll.

Should you try card counting?

Is card counting illegal in the UK? What about Ireland?

It’s important to bear in mind that card counting techniques are not an illegal practice. There is no law which states that casino-goers cannot count cards. However, the sting in the tail is that most land-based casinos take a very dim view to card counting in blackjack. There are countless stories of blackjack players being blacklisted from casinos, which prevents them from ever setting foot in the casino again to try and take advantage of the game.

It’s a similar story over in Ireland, where card counting is not illegal, but Irish casinos reserve the right to remove and ban anyone they suspect of card counting at their blackjack tables. Your chosen offline casino’s approach to card counting will almost certainly be listed in their terms and conditions.

Can you get banned from a casino for counting cards?

Unfortunately, yes. Although card counting in blackjack is by no means against the law, land-based casinos reserve the right to escort you off their premises and ban you from future entry if they believe you are counting cards and attempting to improve your chances of beating the house.

This is why you’ll need to weigh up the pros and cons of adopting card counting techniques at the table. If you enjoy playing at land-based casinos in addition to online, do you really want to run the risk of being banned forever for the sake of a 1-2% edge? Of course, you’ll always be welcome here at Paddy Power Games!

Is it difficult to count cards?

Counting cards in blackjack requires a lot of practice. Not only do you need to be good at maths, but you also need to be capable of filtering out all other possible distractions at the table so you can focus on the running count and on calculating the true count of your game. Even a minor slip of forgetfulness or a miscalculation can result in a flawed blackjack counting strategy.

If you want to increase your chances at winning, learn how to play blackjack from our dedicated article.

Card counting for other card games

Does counting cards work for Poker?

You might be wondering whether any of these card counting techniques can be adopted when playing other casino card games. In truth, there is no way to count cards in poker as you do in blackjack. However, it could be used to help you count the number of outs you have remaining in the deck.

‘Outs’ in poker are the number of unseen cards left in the deck that can improve your hand. This way, you can use probabilities to work out the percentage chance of the card(s) you need appearing from the deck.

For instance, if you have a straight draw, you have a run of four numbers and need the next number to come out on the river (last card). As you have four of the 52 cards on the table, as well as the two you started with in your hand, you can work out the likelihood of the number appearing by dividing 4 by the 46 remaining cards. It’s 4 because there is a card for this number within each suit. 4/46 = 0.087, giving you an 8.7% chance of your number appearing on the turn. This knowledge will allow you to bet accordingly.

Does counting cards work for Baccarat?

Counting cards in the table game of baccarat works more like it does in a game of blackjack. Given that cards are dealt from the dealer’s shoe and the shoe is not shuffled at the end of every hand, it is possible for the result of previous hands to directly influence the probability of winning future hands, at least until the shoe is reshuffled.

Unfortunately, experts on card counting theory such as Thorp believe that card counting in baccarat gives players a negligible benefit, if at all. Although it’s possible to follow one in theory, blackjack players will never be able to make a substantial profit from any card counting system.

✔Is card counting difficult?

Yes, there is no doubt about it. Counting cards in blackjack is by no means a cakewalk. You need to have the mental capacity to focus on the count without being distracted by the environment around you. Further still, you need to consider how many decks of cards you’re playing blackjack with. Card counting in blackjack is hard enough when playing single-deck games but when you factor multiple decks into the equation, it’s an uphill task to stay on track.

It might be a lot easier for you to read about the Blackjack Rules to understand how blackjack works for both the dealer and the player, and practice for free in the demo versions of the game before playing for real money.  

✔How effective is card counting?

The reality is that most highly competent blackjack card counters only gain an advantage of between 0.5-1% over the house. When you consider the potential for significant downswings during lengthy blackjack gaming sessions, there are times when even the best blackjack card counting system doesn’t yield any profit whatsoever. Different types of blackjack games can also limit the effectiveness of card counting techniques too. Consider Spanish 21, for instance, which allows players to split up to four hands and attempt to match the dealer.

✔Can casinos prevent or stop card counting?

It is fair to say that most casinos will do everything in their power to prevent and catch blackjack card counters. They’ll use techniques to put off players from counting such as continuous shuffling machines (CSMs) that render card counting techniques virtually null and void due to minimised deck penetration. Land-based casinos will also use their pit bosses to monitor activity at the tables and attempt to pinpoint potential counters. However, some still claim they manage to go undetected and count cards despite the CSM.  

✔How can you practice card counting?

If you want to know the best card counting system, it’s important to find ways to calculate the True Count of your blackjack game. A rudimentary way to practice card counting is to write numbers one to 30 on pieces of paper and place them in a bag (assuming you want to practice for common six-deck games). Start pulling each number out of the bag and divide the number by six (for the number of decks left in the dealer’s shoe). Do this another time and divide the numbers by five (pretending that one deck has already been used). Keep doing this until you’re dividing by one deck remaining. Mastering your dividing skills is vital to convert running counts into the true count of your game.  

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EV is the expected value in a game. This concept is not unique to the game of blackjack. In fact, it’s commonly used in other casino games like poker, baccarat and craps too. When the EV is a positive figure, this means that you are making a play that is statistically profitable over the long term. Negative EV figures demonstrate the likelihood of your play being a loser, also statistically over the long term.


Although most land-based casinos prohibit card counters from playing at their blackjack tables, that doesn’t mean card counting is a form of cheating. Far from it, in fact. Card counting is a skilful technique; one which requires you to use your brain, in the same way that a successful chess player would think ahead and plot their next moves.

It is a skill to pair optimal blackjack strategy with card counting techniques to help you beat the dealer consistently over the long term. Learning to count cards is not for the faint of heart, but it’s a skill that anyone can grasp with practice.