scorecardresearch Skip to main content
Evan Horowitz

Why counting cards in blackjack can tip the odds

Blackjack is a game where the only winning strategy is to play smart, play long, and play deliberately. David L. Ryan/Globe Staff/File

When Ben Affleck was thrown out of a casino in May for allegedly counting cards, it made for good tabloid news. Somehow, though, Affleck doesn’t fit the stereotype of the card counter. Going back to Dustin Hoffman in “Rain Man” or sensationalized tales of the MIT blackjack team, card counting stories tend to be nerd-revenge narratives, where the uber-sharp outcast uses his underappreciated skills to beat the house and prove his worth.

Affleck is not a nerd. He’s a charismatic celebrity with the acting skill to make his face into a mask. He belongs at the poker table.

What makes blackjack more suited for nerd-revenge is that there’s no bluffing, no intimidation, no necessary artistry. It’s a game where the only winning strategy is to play smart, play long, and play deliberately. If you follow a proven approach, calibrate your bets carefully, and learn how to effectively count cards, you can tip the odds ever so slightly in your favor, and then slowly rack up the winnings.

How is it done?

Basically, the goal is to keep track of which cards have been dealt and which remain in the deck.


If the dealer throws a lot of low cards, then you know there must be a larger-than-normal number of face cards still to come. The more face cards that remain, the better the odds for the player. Among other things, that’s because face cards increase your odds of getting blackjack, raise the likelihood that the dealer will bust, and make it more profitable to double down.

Now, keeping track of every card that comes out is more than most counters can manage, particularly when they’re playing with multiple decks. Instead, they can do what’s called “high-low counting,” where you assign certain point-value to the cards and then track the points.

Low-cards below seven are one point, mid-range cards are zero points, high cards above nine are negative one. As the cards come out, you add up the point values, and keep a running total, which is blandly referred to as “the count.”


For instance, if the first cards are: 7, A, 10, 5, 9, 6, K, 3, K, Q the count would be minus 2, which tells you that more high cards came out than you would ordinarily expect.

Of course, after just one hand, the odds won’t have changed that much. But as you go deeper into the deck, you gain a surer sense for what remains and you can better predict what’s likely to come next.

Is this the only approach?

No, there are lots of ways that sharp blackjack players try to gain an edge. You can improve on the “high-low” method by keeping a separate count of aces, since aces play a special role in blackjack, having two possible values (one or 11). Some players also try “shuffle tracking,” where they follow particular cards through the shuffling process and estimate where they are in the new deck.

How much can this really change the odds?

Even if you’re not counting, blackjack has some of the best odds in any casino. Depending on the rules of the table (which do vary slightly), the house advantage can be as low as 0.5 percent, meaning that on average you lose 50 cents for every $100 you play.

Add card counting to the mix and you can shift the odds in the other direction, so that you’re likely to win 50 cents for every $100 you play. That may not seem like much of an advantage, but given enough time, it lets skilled counters rack up substantial winnings.


Isn’t it illegal to count cards?

Actually, no. Counting cards is perfectly legal, provided you’re not using a computer or other tracking device. When teams of counters work together, they sometime organize as a legal company, with the players as taxable employees.

Do casinos try to stop it?

Oh, yes, they do. Counting may be legal, but that doesn’t mean card counters are welcomed with open arms. Casinos use a number of strategies to control counting.

Change the rules. The main reason card counting works in blackjack is because the house advantage is so low. By changing the rules, casinos can increase the house advantage and ensure that even good card counters still come out behind. Alterations include lowering the payout for blackjack, cutting off the option to “surrender” your hand, and limiting the ability to split or double-down.

Shuffle, shuffle, shuffle. Card counting is all about tracking the deck: what’s come out of the deck and what’s left in the deck. So when casinos mess with the deck, they mess with the count. One way to do this is to reshuffle early, stopping the dealer from getting too deep into the deck. Another is to increase the number of decks being used. Many blackjack games today involve six or even eight decks, and with each additional deck counting becomes less useful. Shuffling, too, stops a counter in his tracks. Every time a deck is shuffled, the odds are reset and the count starts over. Some casinos have “continuous shuffling” machines that reshuffle the cards after every hand.


Kick counters out. In Vegas, at least, casinos are under no obligation to let card counters play. They can’t prosecute them (again, it’s not illegal), but they can limit them to other games or even ask them to leave. Players refer to it as getting “backed off,” and it seems to be what happened to Ben Affleck.

Are there any famous card counters?

Card counting used to be easier. There was a time when you could go into a casino and find a blackjack game with just one deck and dealers who would continue practically to the very last card. One reason it has gotten more difficult is that legendary card counters, and card counting syndicates, exploited these vulnerabilities. And the casinos responded.

There are many colorful tales of successful counters and large counting teams like the Greeks, but perhaps the most famous is the MIT blackjack team. During the 1980s and 1990s, this group of current and former students from MIT and Harvard turned card counting into a profitable business, developing multiplayer strategies that not only helped them win but also helped prevent detection.

Will we be able to count cards in Massachusetts casinos?

The first question is whether Massachusetts will even get casinos. For a while, it seemed quite likely, but recent events have changed the odds. Come November, voters will have the opportunity to decide whether Massachusetts goes ahead with its casino plans or puts a halt to the process.


If the casinos do eventually get built, though, you will be able to count cards there. Whether you can win depends on the rules they establish, how often they shuffle, and how good you are at tracking numbers and adjusting bets, without meeting Ben Affleck’s fate and getting kicked out.

Evan Horowitz digs through data to find information that illuminates the policy issues facing Massachusetts and the United States. He can be reached at Follow him on Twitter @GlobeHorowitz