Blackjack Card Counting

Counting Cards

Counting cards is the most popular and possibly the most practical way to get an edge when playing blackjack. It's a completely legal means of getting an edge over the casino, and it's one of the reasons that blackjack is one of the only beatable casino games on the floor. This page provides a detailed overview of how card counting works, the history of the practice, and some insights into how to get started counting cards for yourself.

You'll probably be surprised at how easy it is to count cards, but once you realize that, you'll also be surprised at how many different ways of counting cards exist. But don't let the number of options scare you away. Counting cards is one of the easiest ways to become an advantage gambler. You don't have to be a genius or a savant. All you have to do is be able to add 1 and subtract 1 from a running count in your head.

How Card Counting Works

In most gambling games, the odds are the same every time you bet. That's because the games have no memory of past occurrences.


If you're playing roulette, there are 38 spaces where the ball can land. If you bet on any single space on the wheel, your odds of winning are 37 to 1. They remain 37 to 1 on every subsequent spin.

But suppose you filled in one of those spaces when a ball landed in it?

The odds of winning on the next spin would become 36 to 1.

And if you kept blacking out spaces, you'd eventually have much better odds of winning that single number bet.

In fact, eventually, when the odds of winning got to be 34 to 1, you'd have a positive expectation bet against the casino. The single number bet pays off at 35 to 1.

All you'd need to do would be to wait until enough numbers had been blocked off the wheel.

Of course, that will never happen at the roulette table, but it happens all the time with a blackjack game.

That's because once a card has been dealt, it can't be dealt again until it's shuffled back into the deck.

You will find games with automatic shuffling machines where the cards get fed back into the deck immediately after each hand. And in those games, it's impossible to get an edge over the casino—at least via counting cards.

But in other games, the odds of winning change based on the composition of the deck.

It's easy to see why with a thought experiment:

Pretend you're playing in a single deck blackjack game where all the aces have already been dealt.

What are your odds of getting a blackjack?
if you said 0%, give yourself a gold star.

You can't get a blackjack without a 10 and an ace. So as each ace and 10 card gets dealt, your chances of getting a blackjack decrease.

Why is this important?

It's important because the payout for a blackjack (or a natural) is 3 to 2, and that's where a lot of the player's expected value comes from.

By the same token, if lots of lower cards have been dealt, and a lot of aces and 10s are still in the deck, you have a better chance of getting a blackjack.

If you raised the size of your bets when you have a better chance of hitting a blackjack, and you lowered the size of your bets when you have a worse chance of hitting a blackjack, you'd probably make more gambling at cards, wouldn't you?

Card counters use a heuristic system to keep track of the ratio of high cards to low cards in the deck. It's simply a matter of assigning a value to the high cards and the low cards and tallying them up as you see the cards get dealt.

The simplest systems just assign the aces and 10s a value of -1 and the 2s through 6s a value of +1.

As you keep a running count, you can raise and lower your bets according to how favorable the deck is.

You can also make changes to the strategy you use to play your hand based on the count.

Both of those actions improve your odds of winning over the long run.

Basic strategy players face a house edge of between 0.25% and 1%, depending on the rules at the casino in question.

But card counters can flip that edge to their side and get an edge over the casino of as much as 1% or 2%.

That doesn't sound like much, but if you're playing for high enough stakes, you can make a little bit of money and have a lot of fun.

And it's way better than the approach most people take when gambling—betting their money, crossing their fingers, and relying on lady luck.

The History of Counting Cards

  • Who invented card counting?
  • How long have been people counting cards?
  • Why do the casinos allow this activity to go on?

We take a look at some of the answers to these questions in this brief history of counting cards.

Many histories of card counting cite Ed Thorp as the inventor of card counting, and that's fair. He did invent what we think of as the "modern" method of counting cards.

But Ed Thorp himself, in his book Beat the Dealer, mentioned several gamblers of his acquaintance who were beating the casinos with various crude card counting methods. But these guys were system players, and it's unclear as to how successful they were. Thorp just doesn't go into that much detail.

But in terms of a mathematically proven card counting strategy to beat the house, Ed Thorp's book is the first and most important example. And even though it was published in 1962, it's still in print, and almost all advantage blackjack players recommend owning and reading a copy of it.

Of course, in the early 1960s, John Scarne was considered the foremost gambling authority in the world. He had addressed blackjack strategy in his book, Scarne's Guide to Casino Gambling, but Thorp had criticized some of that advice as being mathematically incorrect.

Ed Thorp and John Scarne
Thorp and Scarne had a bit of a rivalry, but both of them
contributed mightily to the literature of advantage gambling.

It only took Vegas casinos a couple of years to become terrified of Thorp's methods, so they made a couple of changes to blackjack rules throughout the city. They eliminate the option of splitting aces, which was a huge blow to players. They also only allowed players to double down on a total of 11.

Some well-publicized challenges between Thorp, Scarne, and the casinos made a bit of news, but no one ever accepted anyone's challenges for various reasons. It seems as if the excitement of being able to beat the casino is a news story that recurs every now and then. It was all the news when the book and then the movie Bringing Down the House came out, too.

Casinos began putting countermeasures in place to prevent card counters from getting an edge throughout the 1960s and the 1970s. The most common countermeasure at that time was to increase the number of decks in play. In those days, games with 2 and 4 decks were considered tough. Now, 6 and 8 deck shoes are more or less the standard.

Another development that would matter to the advantage blackjack community was the rise of the Griffin Agency. They were a private investigations company which put together a book of mug shots of known gambling cheats. They eventually included known card counters in these books, which were called The Griffin Book. At one time, they made a fortune selling their services to casinos, but the company has since become defunct.

During these few decades, various teams have engaged in this type of advantage play, too. The most famous of these is the MIT Blackjack Team, which isn't exactly one team at all. In fact, it's several, and there have been several incarnations through the years.

Books on card-counting

Since the 1970s, literally hundreds of books on card counting have been written and published. Some of them, like the books by Stanford Wong, are excellent. Others, like Bringing Down the House by Ben Mezrich, are mediocre at best. (That's the book that made the MIT Blackjack Team a household phrase, at least temporarily.)

You'll find reviews of blackjack books on this page of our site.

Counting cards has even been the subject of court cases. In New Jersey, the courts have ruled that since counting cards isn't illegal, the casinos have no right to bar players suspected of counting. Atlantic City responded by increasing their countermeasures. You won't find anything less than an 8 deck game there, and most games use a continuous shuffling machine, which makes counting impossible.

Is Counting Cards Illegal?

In no jurisdiction of the world that we know of is counting cards illegal. Think about it. How could thinking about the game you're playing be illegal? It's not even cheating.

This doesn't mean that casinos don't reserve the right to run you out of there if they catch you. It's probably more common that they'll just start shuffling up on you a lot more often, though.

But don't worry about getting arrested for card counting. It ain't gonna happen.

On the other hand, if you're using some kind of device to count cards, you ARE cheating, and in most jurisdictions, you're breaking the law. You're not allowed to use devices when gambling in order to get an edge. This includes any kind of portable computer you might try to use to help you count.

We're amazed that people would feel the need to use such a device in the first place. It's not that hard to keep count mentally. It just takes a little bit of practice.

How to Count Cards

The first step in learning how to count cards is to choose a card counting system. We have a page about card counting for beginners which includes information about a simple count called the ace-five count, but it's not as practical or as accurate as it needs to be. It's just good for players who are just getting started.

We recommend that beginners start with the venerable and still useful hi-lo count, which is basically the same counting system used in Thorp's book Beat the Dealer.

Here's how it works:

  • Every time you see a 2, 3, 4, 5, or 6, you add 1 to the running count.
  • Every time you see an ace or any card worth 10, you subtract 1 from the running count.

You need to be comfortable with integers in order to pull this off. If you remember how the number line from middle school math works, you should be fine. If you need a refresher on integers, you can find one here.

This count that you're keeping is called a "running count". If at any time during your session the dealer stops and shuffles up, you need to start your count over from 0.You also need to learn how to convert this running count into a "true count". This takes into account the number of decks in play. To convert the running count into a true count, divide the count by the number of decks you estimate are left in the shoe. This will eliminate the dilutive effect of having so many decks of cards in play.

The point of this count is to determine when you should raise your bets:

  • If the count is 0 or negative, you bet the minimum amount at the table.
  • If the count is positive, you increase the size of your bets in accordance with how high the true count has gotten.

Most players just multiply their minimum bet by the true count number to get the amount to bet.


You're betting $5 per hand.

If the true count is +1, 0, or negative, you bet $5 per hand.

If the true count is +2, you bet $10 per hand.

if the true count is +3, you bet $15 per hand.

The size of your "betting spread" is up to you, but the more you bet when the count is really high, the more of a mathematical edge you get against the casino.

But here's something else to keep in mind. One of the ways that casinos spot counters is by monitoring players who are changing their bet sizes. The lower your spread, the less likely you are to get caught. We've been caught using a spread of 1-10 units, which was admittedly a little aggressive. We've seen counters who limit their top bets to 3X or 5X their minimum bet.

Of course, there are also basic strategy adjustments based on how high or low the count is. These take into account how likely it is that you'll be dealt a high card or low card on the next card, and it also takes into account the likelihood that the dealer has a 10 in the hole or something much lower.

Adjusting your strategy to account for the true count nets you an additional 0.2% to 0.3% against the casino. It's not necessary to change your strategy based on the count, but if you want to milk the casino for every tenth of a percent, you can do so.

Here are some general guidelines based on high and low counts.

Low or Negative count
  • Double less often.
  • Split less often.
  • Hit more often.
Low or Negative count
  • Double less often.
  • Split less often.
  • Hit more often.

The reasons should be obvious, but if the count is low, you're less likely to get a blackjack. That means doubling down and splitting aren't as likely to net you the big payoff that you're hoping for when you put more money into action. It also means that there are a relatively large number of low value cards in the deck, making it less likely that you'll bust if you hit.

On the other hand, if the count is high, you're more likely to get a blackjack. So you want to split and double more often so that you can get more money into action and take advantage of that bigger payout. It also means that you're more likely to get a 10 on your next card, which is likely to bust a lot of hands.

You shouldn't be adjusting your strategy on every move you make, either. Only about 10% of the time do you make these adjustments in your basic strategy.

We generally just rely on bet sizing to provide use with our edge over the casino.

How to Practice Counting Cards

You can't just read the above guide on how to do the hi-lo count and walk into a casino and start counting . This is a skill like any other, and you're going to need to practice. You start by counting through a single deck of cards at your kitchen table.

The hi-lo count is a balance counting system. That means there are as many +1 values as there are -1 values. If you count through a deck of cards using this system accurately, you should end with 0. If you're ending with any other number, start over, concentrate, and keep at it until you can count through a deck one card at a time and get a total of 0 when you finish.

Once you can count through a single deck of cards accurately again and again, start timing yourself. Your goal should be to cut your initial time in half.

Once you've accomplished that, start dealing through the deck in pairs instead of dealing through the cards one at a time. Your goal now is to start recognizing combinations of cards and what their point totals are. For example, if you deal a 2 and a 5 (a "hard 7"), you're looking at a +2. If you deal a 10 and a 2, you're looking at 2 cards which have canceled each other out and count as 0.

Your goal is again to cut the time it takes you to count through the deck in half.

Once you've accomplished this, it's time to start amping up the distractions. Learn to count through the deck accurately with the television on. Try playing the radio and the television at the same time.

Your goal is to be able to count so quickly, accurately, and silently that it requires no effort.You also want to be able to accomplish this without looking like you're concentrating especially hard.

Top Tip

Have someone you trust watch you. Have them point out if you're frowning, if your brow is furrowing, if you're sub-vocalizing and/or moving your lips—anything that might clue the casino in on the fact that you're counting.

You can also practice counting in an online setting, but we think that's less effective than using real cards. After all, you want to duplicate the kind of distracted environment that you'll find in a casino. And you'll also be dealing with regular-sized playing cards at a regular-sized table, so why not practice with the tools you'll actually be using.

Next, you should find a low stakes blackjack game somewhere and practice counting there. At most blackjack tables where there's not a lot of action going on, you can just observe. Try keeping a running count and converting it into a true count when you're not playing. See how comfortable you are with it.

Finally, when you're ready, try playing in as low a stakes game as you can find. Count cards. Get in and get out. You don't want to get busted your first time out. It would be awful to be banned or barred on your first counting session.

How to Avoid Getting Caught

Let's talk a little more about avoiding detection. The easiest way to avoid detection is to not spend a lot of time in any one place. It's tempting when you find a juicy game to stay there forever, but that's the opposite of what you should do.

In Sklansky on Blackjack, David Sklansky provides the following advice about avoiding detection:

  • Don't play at the same casino more than once a day—or maybe even more than once a week.
  • Don't play there during the same shift every day.
  • Don't play with the same dealers every day.
  • Don't spend more than an hour at any given table at any given casino at a time.

These all seem like sensible guidelines to us, but we have a few more suggestions:

  • Don't give advice to the other players at the table.
  • Don't deviate from basic strategy too much.
  • Pay attention to how much attention the casino staff are paying to you. If you think you're being watched, get out of there.
  • Don't concentrate too hard.
  • Tip the dealer occasionally. Counters are notorious for not tipping, as it cuts into their expectation.
  • Don't drink alcohol, but do have a drink in your hand. We always order a club soda with lime in a short glass. It looks like an alcoholic drink, but your mind will stay sharp.
  • Avoid looking nerdy in any way. You don't want to look like a mathematician. You want to look like a country bumpkin or a city slicker, but not a brainy type.

Don't stress out too much about avoiding detection. Scenes of violence in modern casinos are rare. The industry is too well-regulated. The worst case scenario is that you'll be escorted off the premises.

On the other hand, if you want to read some interesting stories about encounters between blackjack players and dealers during a less civilized age, check out Lawrence Revere's books on blackjack. The World's Greatest Blackjack Bookby Lance Humble also contains some interesting stories.

And if you're just looking for drama related to counting cards, check out Ben Mezrich's book, Bringing Down the House. It's completely different from the movie, but it's no less melodramatic. It's also (admittedly) inaccurate about the details of what really happened, which is disappointing. We've found that the true stories are almost always more interesting than the fictionalized versions.

Various Systems for Getting an Edge

The hi-lo system is only one way of counting cards. Numerous methods exist, all of which have interesting names. Each of these systems have advantages and disadvantages, pros and cons. We provide a broad overview of the most popular systems below, but each of these link to a page describing that particular system in more detail.

First, a word about types of card counting systems. They can be categorized in multiple ways, but two that matter follow:

  • 1 Balanced versus unbalanced

    A balanced system has the same number of points for low value cards as it does high value cards, so that when you count through a deck, you always finish with 0. An unbalanced system does not. Unbalanced systems are often used to eliminate the need for a running count to true count conversion.

  • 2 Single level versus multi level

    A balanced system has the same number of points for low value cards as it does high value cards, so that when you count through a deck, you always finish with 0. An unbalanced system does not. Unbalanced systems are often used to eliminate the need for a running count to true count conversion.

When you click through to the detailed description of each system below, you'll find information about these 2 categories and how they apply.

The goals of different systems vary. Some have a goal to just be easy to use. Others focus on offering the best edge when making basic strategy adjustments. Others shoot for a strong betting correlation. We discuss how each system meets those criteria in the individual articles, too.

Hi-Lo System

This is the most basic and probably 2nd easiest counting system to learn. We describe it in some detail on this page, but we go into exhaustive detail on the page devoted specifically to that system.

Read more on the Hi-Lo System K-O (Knockout) System

The K-O or Knockout System is an unbalanced system that eliminates the need to convert the running count into a true count. They do this by starting the count at a negative number and unbalancing the count.

Read more on the Knockout System Hi-Opt I and Hi-Opt II Systems

These are the systems promoted in Lance Humble's book, The World's Greatest Blackjack Book.

Read more on the Hi-Opt Systems Wong Halves System

This is one of the most accurate systems to use, but it's also harder to use than most. It doesn't use whole numbers. 2s and 9s, for example, are worth +0.5 and -0.5, respectively. This increases the count's accuracy, but it makes it harder to implement.

Read more on the Wong Halves Systems Omega II System

This system is found in Bryce Carlson's book, Blackjack for Blood. It's relatively hard and requires you to keep a side count of aces.

Read more on the Omega II Systems Zen System

This one comes from Arnold Snyder's book, Blackbelt in Blackjack (which is one of the best books on the subject, in our opinion.) It's more accurate than the Hi-Lo System, but it's also harder to implement. Some cards are worth 1 and some are worth 2, which makes it a "multi level" system.

Read more on the Zen System Red 7 System

This strategy is as easy as the Hi-Lo System. Like the K-O System, it also eliminates the need for a running count to true count conversion. It's also found in Arnold Snyder's book, Blackbelt in Black, which we can't recommend too highly. It's probably our favorite blackjack book.

Read more on the Red 7 System Canfield Expert and Master Systems

The Canfield Expert is an older system from the 1970s that was used mostly in single deck games. It's easy to use but probably not as effective as newer counts with a similar level of difficulty. The Master system is much harder and not as effective as it should be given its difficulty.

Read more on the Canfield Systems Kiss 2 and Kiss 3 Systems

These counts are unusual in that they keep up with suits as well as point values. These are surprisingly powerful and easy counts to use. They're explained in detail in Renzey's Blackjack Bluebook II.

Read more on the KISS Systems Mentor System

This is a system that's used mostly for multi deck games. It's featured in Renzey's Blackjack Bluebook II.

Read more on the Mentor System REKO System

This is Norm Wattenberger's improvement to the K-O System mentioned earlier.

Read more on the REKO System Revere Systems

Lawrence Revere was one of the great characters in the game of blackjack. He published several books himself, but the most entertaining material ABOUT him can be found in Lance Humble's The World's Greatest Blackjack Book. Most of his systems are harder than they need to be.

Silver Fox System

This is a proprietary system that used to be available from Ralph Stricker.

Read More on the Silver Fox System UBZ a System

This is also called the "Unbalanced Zen Count". It's another proprietary system.

Read more on the UBZ2 System Uston Systems

Ken Uston also had several counting systems. They seem hard.

Please Note

Much of the information about the various systems above was learned reading QFIT, which is an excellent resource, and we're in Norm Wattenberger's debt for the information he provides there.


Counting cards is a completely legal way to get an edge over the casino, and the great thing about it is that it's not really that hard to do. That being said, learning how requires a certain amount of dedication. But if you can add or subtract 1 repeatedly, you can count cards in blackjack.

The practice has an interesting history, and it's recently caught the public eye again because of the movie Bringing Down the House.

Casinos are wise to how counters get an edge, and they're good at thwarting suspected advantage players.

This doesn't mean you can't get an edge playing blackjack

It just means you have to be sensible and smart. Don't be obvious about what you're doing. And don't camp out at one place for hours on end or hit the same casino at the same time every day of the week.

You'll get most of your edge by raising and lowering your bets based on the ratio of high cards to low cards in the deck, but you can get another 0.2% or 0.3% by adjusting your strategy decisions about 10% of the time. The rule of thumb is to hit more often when the count is low, but double down and split less often. You do the opposite when the count is high.

Lots of people still beat the casinos on a regular basis. With a little bit of study and effort, you too can become a card counter. It just takes a little bit of practice.

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