Card counting in blackjack: the Hi-Lo count and the true count

What card counting is

Card counting is a way of tracking which cards have already been dealt, so you know what is left in the shoe. You do not memorize every card. You keep one running number in your head, and that number tells you whether the cards still to come are rich or poor in tens and aces.

That matters because the mix of cards left changes how good each play is. When the remaining cards are rich in tens and aces, a hit on a stiff hand is more likely to bust, a double down is more likely to land on 20 or 21, and the dealer is more likely to have blackjack under an ace. Counting lets you spot the few hands where that shifts the best play away from basic strategy.

Card counting is legal. It is a mental skill that uses only the cards every player at the table can see.

Hi-Lo card values

Hi-Lo is a simple, widely taught counting system, and it is the one the Blackjack Trainer app teaches. Every card gets one of three values:

• 2, 3, 4, 5, 6: +1. When low cards leave, what remains leans toward tens and aces.
• 7, 8, 9: 0. These barely change the mix, so they count for nothing.
• 10, jack, queen, king, ace: -1. When these leave, what remains leans toward small cards.

• +12♠︎3♥︎4♣︎5♦︎6♠︎2 to 6
• 07♠︎8♥︎9♣︎7 to 9
• −110♠︎J♥︎Q♣︎K♦︎A♠︎10 to ace

Hi-Lo is a balanced count

Each deck has twenty +1 cards and twenty -1 cards, so counting a full deck from start to finish always lands on zero. That gives you a built-in way to check your own accuracy.

How to keep the running count

Start at zero after every shuffle. As each card is turned face up, add its value to your total. That total is the running count. Count every card you see: your own, the other players' cards, and the dealer's hole card when it is turned over.

Example: the cards 5, king, 2, 9, ace, 3, 6 come out. Their values are +1, -1, +1, 0, -1, +1, +1, so the running count is +2.

Two habits make it faster. First, cancel pairs: a low card and a ten-value card together count zero, so you can skip both. Second, learn to read common pairs by sight, so that a king and a 4 register as 0 without any arithmetic.

The true count

A running count means little until you know how many cards are left. A running count of +6 with one deck to come is a strong lean toward tens and aces. The same +6 with six decks to come is barely a lean at all. The true count adjusts for that:

• True count = running count ÷ decks remaining.
• Running count +6 with 3 decks left: true count +2.
• Running count +5 with 2 decks left: true count +2. Drop the fraction toward zero, so +2.5 reads as +2.
• Running count -7 with 2 decks left: true count -3.

Estimating decks remaining

Judge how many decks have been played by looking at the discard tray, not the shoe, and take that from the number of decks the game started with. Half a deck is as fine as you need. In a one-deck game, the running count at the top of the deck already is the true count.

Conventions differ on rounding. This site and the app drop the fraction toward zero, which never overstates the count. Whichever convention you choose, use it every time.

How the count changes your play: index plays

Basic strategy assumes a neutral shoe. The count tells you when the shoe is not neutral, and for a small set of hands the best play flips at a particular true count, called the index. Each index play names a hand, the index, and the play to make at that true count or higher. Below the index, you make the other play.

The best-known list is the Illustrious 18, published by Don Schlesinger. These 18 plays carry most of the value of changing your play with the count. Here are ten of them, using the published Hi-Lo values for a six-deck game where the dealer stands on soft 17:

• Insurance: take it at +3 or higher. Below +3, decline it as usual.
• Hard 16 vs 10: stand at 0 or higher, hit below 0.
• Hard 15 vs 10: stand at +4 or higher, hit below +4.
• Hard 12 vs 3: stand at +2 or higher, hit below +2.
• Hard 12 vs 2: stand at +3 or higher, hit below +3.
• Hard 12 vs 4: stand at 0 or higher, hit below 0.
• Hard 13 vs 2: stand at -1 or higher, hit below -1.
• Hard 11 vs ace: double down at +1 or higher, hit below +1.
• Hard 10 vs 10: double down at +4 or higher, hit below +4.
• Hard 9 vs 2: double down at +1 or higher, hit below +1.

Surrender and the soft 17 rule

The stand plays for hard 16 and hard 15 against a 10 apply where surrender is not offered. With late surrender, basic strategy surrenders both hands, and hard 15 against a 10 switches to a hit when the true count drops below 0.

When the dealer hits soft 17, a few of these numbers shift, and hard 11 against an ace is already a double down in basic strategy.

Why the play flips

• Insurance wins only when the dealer has blackjack. At +3 or higher, the remaining cards hold enough tens to make it the right call.
• Hard 16 vs 10: a shoe rich in tens makes a hit more likely to bust, so standing becomes the better play.
• Hard 12 vs 3: extra tens make your hit more likely to bust and the dealer's own draw more likely to bust, so standing gains.
• The doubles: with more tens and aces left, your one card is more likely to land you on 20 or 21.

Learn basic strategy first

Index plays only help once you make every basic strategy play without thinking. Index spots come up rarely, while basic strategy decisions come up on every hand, so mistakes there matter more. Learn the chart first, then the count, then the index plays.

How to practice counting

Build the skill in steps, and get accurate before you get fast:

• Count down a single deck one card at a time, and check that you finish on zero.
• Deal two cards at a time and cancel pairs as you go.
• Practice converting: take a running count and a decks-remaining figure, and give the true count without stopping.
• Count while you play hands, so the count runs alongside your basic strategy decisions instead of replacing them.