Card counting is a way of tracking the high and low cards that have already been dealt so you know when the rest of the shoe favors you, then betting more in those spots. Done well, with the right game, bet spread and bankroll, it turns blackjack’s house edge into a player edge of about 1%. It is legal in the US as long as you use only your head, but casinos can and do act against counters.
Card counting at a glance
| Item | Detail |
|---|---|
| Most common system | Hi-Lo: 2 to 6 count +1, 7 to 9 count 0, 10s and aces count -1 |
| Typical edge for a skilled counter | About 1% in six-deck games |
| How often the count favors you | Roughly 10% to 35% of hands, depending on rules and penetration |
| Bankroll rule of thumb | About 100 times your maximum bet |
| Legal? | Yes, without devices; casinos may still restrict counters |
What is card counting?
Card counting is a mental technique for keeping track of the cards that have been dealt since the last shuffle. You do not memorize every card, which is a myth popularized by the 1988 film Rain Man. You keep a single running number that tells you whether the cards still to come are rich in high cards or low cards. The MIT blackjack team used counting together with team play, with spotters signaling a big bettor to join tables when the count was high, and its story inspired the film 21.
Why high cards help the player
A shoe with lots of 10s and aces left helps the player in several ways:
- More blackjacks. You and the dealer both get more naturals, but your blackjack pays 3:2 while the dealer’s only wins your bet. On a $100 bet, a dealer blackjack costs you $100 and yours pays $150. That is also why you should avoid 6:5 blackjack, which takes much of that bonus away.
- Better doubles and splits. Doubling down and splitting win more often when the next card is likely to be a 10.
- More dealer busts. When the dealer shows a 2 to 6 and has to draw, a 10-rich shoe makes a bust more likely.
- Profitable insurance. At high counts, insurance against a dealer ace becomes a good bet.
A shoe full of small cards does the opposite: fewer blackjacks, weaker doubles and fewer dealer busts.
Master basic strategy first
Card counting is not where to start. First you need basic strategy, the mathematically best play for every combination of your hand and the dealer’s upcard. Counters play most of their hands by basic strategy, so it has to be automatic. If you are still thinking about whether to hit, you cannot keep the count at the same time.
Two examples many players get wrong: you should hit hard 16 against a dealer 10 (or surrender if the table allows it), and you should split a pair of 9s against a dealer 8 rather than standing on 18. Strategy changes slightly with the number of decks, whether the dealer hits or stands on soft 17, and whether you can double after splitting, so learn the chart for the game you play. Any good blackjack book has a basic strategy section, and flashcards or a training app are the fastest way to drill it.
How to count cards with Hi-Lo
Hi-Lo is the most widely used counting system and the best one to learn first. Take a single deck and start at 0. Turn the cards over one at a time:
- For every 2, 3, 4, 5 or 6, add 1.
- For every 10, jack, queen, king or ace, subtract 1.
- For every 7, 8 or 9, do nothing.
If a 5 and a 6 come out, the count is +2. If a king follows, it drops to +1. Hi-Lo is a balanced count: there are as many +1 cards as -1 cards, so if you count a full deck correctly you finish at exactly 0. That is a good way to check yourself while you practice. Serious counters work at it until they can count down a deck quickly and without mistakes.
A high positive count means the remaining cards are rich in 10s and aces, and you raise your bet. A negative count means the house has a bigger edge than usual, so you bet the minimum or skip hands if the table allows it.
Running count and true count
The number you keep in your head is the running count. In a six-deck shoe, a running count of +6 means much less with five decks still to be dealt than with one. To adjust for this, counters convert to the true count by dividing the running count by the number of decks left. A running count of +6 with three decks remaining is a true count of +2. Bets and strategy changes are based on the true count.
Some systems are unbalanced, meaning the card values do not cancel out over a full deck. They are designed to skip the true count conversion, which makes them easier to use, at some cost in accuracy.
What separates a winning counter from a losing one
Learning the count is the easy part. Winning with it takes several other skills:
Strategy deviations
Counters change some basic strategy plays when the true count is high or low. These changes are called index plays. The most valuable is insurance, which is a bad bet off the top but a good one when the count is high enough. Others cover common hit, stand, double and surrender decisions.
Bet spread
Counting only makes money if you bet much more when the count is good than when it is bad. In multi-deck shoe games the count is favorable only a minority of the time, roughly 10% to 35% of hands depending on the rules and penetration, so a counter who barely raises their bet gains little or nothing.
Game selection
Rules and penetration matter. Penetration is how deep into the shoe the dealer goes before shuffling; the deeper, the more often useful counts come up. A game with good rules and deep penetration is worth far more to a counter than one that shuffles early or pays 6:5.
Bankroll
Even with an edge, the swings are large. A common rule of thumb is a bankroll of about 100 times your maximum bet. Underfunded counters often go broke during a normal losing streak, long before their edge has time to show.
How much can a card counter win?
Less than most people think. A skilled counter in a six-deck game typically has an edge of about 1%. At an average bet of $100 and 50 hands an hour, that works out to roughly $50 an hour on average, with very large swings up and down. It is a grind that takes many hours of play before the edge shows up in your results.
Is card counting legal?
Yes. Counting cards in your head is not illegal under US federal, state or local law. Using a device or an outside helper to count is a different matter and can be a crime.
Casinos still don’t like counters. In most places, including Nevada, a casino can ask a suspected counter to stop playing blackjack or to leave. New Jersey is a notable exception: a 1982 New Jersey Supreme Court ruling in a case brought by card counter Ken Uston held that Atlantic City casinos cannot bar players simply for counting, so casinos there rely on countermeasures instead.
How casinos fight card counting
- Shallow penetration: shuffling earlier so fewer cards are dealt.
- Continuous shuffling machines: cards go back into the machine after each round, which makes counting almost worthless.
- Rule changes: such as 6:5 blackjack payouts or no mid-shoe entry.
- Flat-betting limits and back-offs: limiting bet changes or barring suspected counters from blackjack where the law allows.
For more on this kind of play, see our guide to becoming a casino advantage player. For rules and odds of other table games, browse our casino games guides.
Card counting FAQ
Is card counting illegal?
No, as long as you count in your head without devices or outside help. Casinos can still restrict or bar counters in most states.
What is the easiest card counting system?
Hi-Lo is the most common place to start: +1 for 2 to 6, 0 for 7 to 9 and -1 for 10s and aces.
How much of an edge does card counting give?
About 1% for a skilled counter in a typical six-deck game, with good bet spreading.
Does card counting work against a continuous shuffling machine?
No. The machine keeps the cards so close to freshly shuffled that counting gives almost no advantage.
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