Introduction
Every card dealt from a shoe shifts the probability landscape. The Hi-Lo system gives you a simple framework to track these shifts: assign a value to each card, keep a running total, and you’ll always know whether the remaining deck favors high cards or low cards.
This is the foundation of probability tracking — and the first skill you’ll master with 21 Sharp.
How the Hi-Lo System Works
The Hi-Lo system divides the 13 card ranks into three groups, each assigned a tracking value:
| Cards | Value | Reason |
|---|---|---|
| 2, 3, 4, 5, 6 | +1 | Low cards leaving the deck increase the proportion of high cards remaining |
| 7, 8, 9 | 0 | Neutral — these cards don’t significantly shift the probability balance |
| 10, J, Q, K, A | -1 | High cards leaving the deck decrease the proportion of high cards remaining |
As each card is revealed, you add its value to your running total. This total — the probability index — tells you the current state of the deck.
Why the System is Balanced
A standard 52-card deck contains:
- 20 low cards (four each of 2-6): 20 × (+1) = +20
- 12 neutral cards (four each of 7-9): 12 × (0) = 0
- 20 high cards (four each of 10-A): 20 × (-1) = -20
Total: +20 + 0 + (-20) = 0
This is what makes Hi-Lo a balanced system. If you count through an entire deck accurately, you’ll always end at zero. This property is the basis of the deck countdown drill — a self-test for accuracy.
Worked Example
Imagine these five cards are dealt from the shoe:
7♠, K♥, 4♦, 5♣, A♠
Let’s track the probability index:
| Card | Value | Running Total |
|---|---|---|
| 7♠ | 0 | 0 |
| K♥ | -1 | -1 |
| 4♦ | +1 | 0 |
| 5♣ | +1 | +1 |
| A♠ | -1 | 0 |
After these five cards, the probability index is 0 — the deck is neutral. No advantage to either side.
Now imagine instead:
3♥, 5♦, 6♣, 2♠, 4♦
| Card | Value | Running Total |
|---|---|---|
| 3♥ | +1 | +1 |
| 5♦ | +1 | +2 |
| 6♣ | +1 | +3 |
| 2♠ | +1 | +4 |
| 4♦ | +1 | +5 |
A probability index of +5 is significant. Five low cards have left the deck, meaning the remaining cards are disproportionately high. Statistically, the deck now favors the player.
Practice Exercises
Try counting these sequences yourself before checking the answer:
Sequence 1: 10♣, 3♦, 8♠, K♥, 5♣, 2♦, A♠, 9♥
Answer
(-1) + (+1) + (0) + (-1) + (+1) + (+1) + (-1) + (0) = 0
Sequence 2: 2♥, 3♠, 4♦, 5♣, 6♥, 7♠, 8♦
Answer
(+1) + (+1) + (+1) + (+1) + (+1) + (0) + (0) = +5
Sequence 3: A♠, K♦, Q♣, J♥, 10♠, 9♦, 8♣
Answer
(-1) + (-1) + (-1) + (-1) + (-1) + (0) + (0) = -5
Key Takeaways
- The Hi-Lo system assigns +1 to low cards (2-6), 0 to neutral cards (7-9), and -1 to high cards (10-A)
- A positive probability index means more low cards have been dealt — the remaining deck is rich in high cards
- A negative index means more high cards have been dealt — the remaining deck is rich in low cards
- Hi-Lo is a balanced system: counting a full deck always totals zero
- This is the most widely taught and recommended starting system for beginners
Next Steps
Once you can assign values without hesitation, move on to understanding the probability index — where you’ll learn what the running total actually means for decision-making.
Practice in the 21 Sharp app with the Index Trainer drill to build speed and accuracy.