How can someone use basic arithmetic to gain an edge over a casino, then get told they can never play there again? That is the odd world of card counting. The math is simple, the edge is small, and the casino's response is fast.
What is card counting in blackjack?
Card counting is a way to track which cards have left the deck, so you know when the cards still to come favor you. Blackjack is different from roulette or slots because the game has memory. Every card dealt changes what is left. When the remaining cards hold extra tens and aces, the player wins a little more often and gets paid 3 to 2 on a blackjack. When they hold extra small cards, the dealer does better.
A counter does not memorize the order of cards. They keep one running number in their head and use it to decide how much to bet. Mathematician Edward Thorp first showed that this works in his 1962 book Beat the Dealer, and the method has been taught ever since. You can see how this ties to the house edge: blackjack has one of the lowest edges in the casino, which is why a counter can flip it.
How does the Hi-Lo count work?
In Hi-Lo, every card gets a value: +1 for 2 through 6, 0 for 7 through 9, and -1 for tens, face cards and aces. You add each value as the card is dealt. Low cards leaving the shoe are good for you, so they add. High cards leaving are bad for you, so they subtract.
| Cards | Hi-Lo value | What it means |
|---|---|---|
| 2, 3, 4, 5, 6 | +1 | Low cards gone, shoe gets richer in tens and aces |
| 7, 8, 9 | 0 | Neutral |
| 10, J, Q, K, A | -1 | High cards gone, shoe gets poorer |
A positive total means the cards left lean high, which helps the player. A negative total helps the dealer. Hi-Lo is the most common system because it is easy, not because it is the strongest one.
What is the difference between running count and true count?
The running count is the raw total, and the true count is that total divided by the number of decks left in the shoe. The division matters because a running count of +6 means very little with six decks left, but a lot with one deck left.
For example, if the running count is +6 and three decks remain, the true count is +2. Counters raise their bets as the true count climbs and bet the table minimum when it is low. They also change a few playing decisions, such as when to take insurance or stand on a stiff hand.
Try it yourself below. Tap each card as it is dealt, set the decks left, and watch both numbers.
Hi-Lo running count and true count
Tap a card each time it is dealt. Nothing is sent anywhere, this runs in your browser.
Count is neutral. A counter would bet the table minimum.
Note that the true count only helps if you estimate the decks left. Counters judge that by eye from the discard tray, which is a skill of its own.
How big is the edge for a card counter?
A disciplined counter gains roughly 0.5 to 1.5 percent over the house, according to the Wizard of Odds. Wikipedia describes about 1 percent in a typical six-deck game. With basic strategy alone, the house keeps an edge of around half a percent, so counting turns a small loss into a small win.
That edge is thin. A player betting $100 a hand for 50 hands an hour would earn around $50 an hour at a 1 percent edge, and results swing hard from session to session. Counters need a large bankroll, good discipline and hundreds of hours before the math shows up as profit. The movie version, where one hot streak makes you rich, is not how it goes. If you want the numbers behind that kind of swing, see what variance means in iGaming.
Is card counting illegal?
No. In most places, counting is legal because it uses only your memory, and you are not cheating or touching the cards. Using a device to count is a different matter and is illegal in many US states.
But casinos are private businesses, and in most places they can refuse to let you play. That is why counters get "backed off": a manager tells them they may play anything except blackjack, or asks them to leave.
New Jersey is the exception. In Uston v. Resorts International (1982), the state Supreme Court held that only the Casino Control Commission can set the rules of play, so a casino cannot exclude a patron for using a strategy the rules allow. The casino can still shuffle up when it sees a counter, but it cannot bar them.
How do casinos fight back against card counters?
Casinos use a mix of game design and people watching. The main tools are:
- Continuous shuffling machines (CSMs). The discards go straight back into the shoe, so the count never builds. Counting is close to useless on these tables.
- Shallow dealing. A cut card is placed early in the shoe, so the dealer reshuffles before a count gets big. Counters want deep dealing, which casinos limit.
- Shuffling when the count is high. Staff may shuffle right after a counter raises their bet.
- Watching bets. A player who bets $10 and then jumps to $200 at the same moments the count rises stands out. Software and surveillance teams look for that pattern.
- Backing off or banning. Outside New Jersey, a casino can tell a suspected counter to stop playing blackjack, or to leave for good.
Counters answer with cover play: smaller bet spreads, team play, and moving between casinos. The best known example is the MIT blackjack team and its Gorilla strategy, which used teammates to hide the counter's behavior. Card counting is also one kind of advantage play, like the edge sorting method Phil Ivey used in baccarat, though the law treats the two very differently.
Can you count cards in online blackjack?
Not in standard online blackjack. RNG-based games use software to shuffle a full deck before every hand, so the cards already seen tell you nothing about the next ones. You can read how that works in RNG testing.
Live dealer blackjack deals real cards, but most tables use automatic shufflers or reshuffle early, so counting rarely pays. That is one reason operators are comfortable running blackjack with a low house edge. It is also why side bets, which carry a much higher edge, are pushed so hard: counting does not help on them the way it does on the main hand.
The bottom line
Card counting is real, legal in most places, and worth about 0.5 to 1.5 percent to a disciplined player. Casinos know this, so they limit it with shuffling machines, shallow dealing and the right to ask a counter to leave. For online operators, the lesson is that RNG games remove the problem completely, and live tables can be set up to keep it small.
If you are building an online casino and want blackjack that works the same for every player, see pricing for what launching a white-label casino platform costs today.
Key takeaways
- Card counting is a bookkeeping method that tracks whether the cards left in the shoe favor the player or the dealer, and it uses no device and no cheating.
- In Hi-Lo, cards 2 to 6 are +1, cards 7 to 9 are 0, and tens and aces are -1, so a high count means the shoe is rich in tens and aces.
- The running count must be divided by the number of decks left to get the true count, which is the number that tells you how big to bet.
- A realistic counter gains about 0.5 to 1.5 percent over the house, which needs a large bankroll and hundreds of hours of play to show up as profit.
- Counting is not a crime in most places, but casinos can refuse service, shuffle early or bar you, while New Jersey casinos cannot bar counters after the 1982 Uston v. Resorts ruling.
- Online RNG blackjack reshuffles every hand, so there is nothing to count, and most live dealer games use shuffling machines or shallow dealing that defeat counting too.
