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How to Count Cards in Blackjack

If you’re going to take down the house at the blackjack table, you need to be an expert at counting cards. Despite what pop culture may make you believe, however, you don’t need a photographic memory or superhuman smarts to master card counting. All you need is focus, determination, and plenty of practice.

Basically, counting cards work because blackjack results are governed by non-independent events. In contrast to other forms of gambling like slots, roulette, or craps—games where the outcome of each pull, spin, or roll has no effect on any of the outcomes that follow—the probability of different cards coming up in a blackjack game is constantly in flux, based on which cards have come before.

For instance, if you’re playing blackjack with a single deck and all four aces come out at the beginning of the game, then you know that you’re never going to see another ace until the dealer shuffles. The actual practice of counting cards is only slightly more complicated.

The Hi-Lo System for Counting Cards in Blackjack

We start by assigning values to different cards. The low cards, 2-6, are worth +1, the high cards, T-A, are worth -1, and 7-9 are neutral (0).

Photo: mathismeth

Then keep a running count for every card until the dealer shuffles. If, for example, you see TJA38 to start, we count it -1-1-1+1+0=-2.

As the count goes more positive, the player has the advantage because it means there are more high cards left in the deck. As the count goes negative, the opposite is true: the advantage goes to the house.

Calculate the True Count

Now that we have our running count, we need to figure out the “true count”, which is the running count divided by the number of decks left to be dealt. If we have 5 decks remaining and a running count of 15, then the true count is 3.

From there, we can use the true count to make better, more profitable decisions at the table. Bet little or nothing when the true count is low, and bet proportionally more when it increases. In general, you want to bet according to this formula:

True count – 1 betting unit.

Let’s put it into context and say that the running count is 20 with 5 decks remaining. The true count is 20/5=4. We then do 4-1=3 units for our optimal bet. If the betting unit is 100 chips, the best play would be to bet $300 in this situation (so long as you have the right hand!)

The last thing to remember is that counting cards doesn’t tell you whether or not it’s a good idea to bet in a given situation—that comes down to basic strategy. Counting cards will tell you how much to bet if it’s a good situation to bet on.

It may seem like a lot to pay attention to all at once, but as you practice and improve, it will become second nature.


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