True Count Explained: Why Dividing by Decks Changes Everything

If you've read anything about card counting, you've encountered two terms: running count and true count. Most explanations stop at "divide by decks remaining."

That's technically correct, but it misses why this matters—and understanding the why is what separates tourists from advantage players.

The Running Count Problem

Let's say you're using the Hi-Lo system. You've been tracking cards and your running count is +6. Great news, right? The deck is favorable!

Not necessarily.

A running count of +6 means you've seen six more low cards (2-6) than high cards (10-A). But the significance of this imbalance depends entirely on how many cards remain.

Consider two scenarios:

Scenario A: Running count +6, one deck remaining (52 cards)

Scenario B: Running count +6, six decks remaining (312 cards)

In Scenario A, those extra six high cards are concentrated in just 52 cards. In Scenario B, they're diluted across 312 cards.

The running count is identical. The advantage is not.

What True Count Actually Measures

True count normalizes the running count to a per-deck basis:

True Count = Running Count ÷ Decks Remaining

For our examples:

• Scenario A: TC = +6 ÷ 1 = +6
• Scenario B: TC = +6 ÷ 6 = +1

Now the difference is obvious. A true count of +6 is a significantly favorable situation. A true count of +1 is barely above neutral.

The Probability Behind It

Let's get concrete. In a neutral deck, the probability of the next card being a 10-value card is:

16 ten-value cards ÷ 52 total cards = 30.77%

When the true count is +1, the deck is slightly rich in high cards. The approximate probability shift:

Base probability + (TC × ~0.5%) = 30.77% + 0.5% ≈ 31.3%

At TC +6:

30.77% + (6 × 0.5%) ≈ 33.8%

That 3% difference compounds across multiple draws in a hand, particularly for situations like:

• Dealer showing a stiff hand (2-6) and having to draw
• Your chances of getting a 10 on a double down
• Probability of blackjack (which pays 3:2)

Why Casinos Use 6-8 Deck Shoes

This is where casino countermeasures become clear.

With a single deck, the true count moves dramatically with each card. Remove four 10s in the first few hands, and your true count might swing to +2 or +3 quickly.

With eight decks, those same four 10s barely register. The count moves sluggishly. You need massive imbalances before the true count becomes significantly positive or negative.

Here's a table showing how many excess low cards you need to reach TC +2:

In an 8-deck shoe at mid-penetration, you need to have seen twelve more low cards than high cards just to reach TC +2. That takes time—time during which you're grinding at near-zero EV.

Estimating Decks Remaining

In a physical casino, you can't count the exact cards remaining. You estimate by looking at the discard tray.

Most shoes hold cards face-up in the discard. A standard deck is about 2cm thick. You're eyeballing:

• 2cm in discard = ~1 deck dealt, 5 remaining (in 6-deck shoe)
• 6cm in discard = ~3 decks dealt, 3 remaining
• 10cm in discard = ~5 decks dealt, 1 remaining

This imprecision is why professional counters practice. A 10% error in deck estimation translates to a 10% error in your true count calculation.

True Count and Bet Sizing

This is where true count translates to money.

The standard rule of thumb: your edge increases by approximately 0.5% for each +1 true count.

The exact multipliers depend on your bankroll, risk tolerance, and casino heat concerns. But the principle holds: you're betting in proportion to your advantage.

At TC 0, you're not favored. At TC +5, you have a 2% edge on every hand. The rational response is dramatically different bet sizes.

True Count and Strategy Deviations

Bet sizing is the primary use of true count, but it also affects optimal strategy.

Basic strategy assumes a neutral deck. When the count is extreme, some decisions flip:

Insurance: Basic strategy says never take insurance. But at TC +3 or higher, the deck is so rich in 10s that insurance becomes a positive EV bet.

Standing on 16 vs 10: Basic strategy says hit. At TC +1 or higher, the increased probability of busting (and the increased probability the dealer has a 10 underneath) makes standing correct.

Doubling on 10 vs 10: Basic strategy says hit. At TC +4, the abundance of 10s makes doubling optimal.

These are called "index plays" or "strategy deviations." Professional counters memorize a set of them (typically the 18-20 most valuable) and adjust their play accordingly.

The True Count Theorem

There's a mathematical theorem that underlies all of this, sometimes called the True Count Theorem:

The expected value of your next bet depends only on the true count, not on the specific cards that created it.

This is profound. It means you don't need to track which specific cards were dealt—just the running count and decks remaining. A true count of +3 has the same EV whether you got there by seeing twelve 5s and nine Aces, or fifteen 3s and twelve Kings.

The theorem holds because your EV depends on the proportion of remaining high cards to total cards, which is exactly what true count measures.

Practical Calculation Speed

In a real casino, you have maybe 2-3 seconds between hands to:

1. Update your running count (add all cards from the last hand)
2. Estimate decks remaining
3. Calculate true count
4. Decide your bet for the next hand

This is why counters drill. The arithmetic needs to be automatic.

Common shortcuts:

• Cancellation: A 5 (+1) and a King (-1) cancel to zero. Look for pairs.
• Anchor numbers: Remember that 6 decks = 312 cards, half-shoe = 156 cards = 3 decks.
• Rough division: You don't need precision. TC +2.7 vs TC +3 doesn't change your bet.

Why This Matters Even If You Never Count

Understanding true count transforms how you think about blackjack.

When you see someone betting big and winning, you might think they're lucky. Maybe. Or maybe they're betting big because the count justified it, and the favorable deck delivered the expected results.

When a casino shuffles early, you'll understand why. They're resetting the count to zero, eliminating any player advantage that might have developed.

When someone says "the cards are hot" or "the cards are cold," you'll understand what they're actually (unconsciously) describing: short-term variance around a positive or negative count.

Blackjack isn't random. The probabilities shift with every card. True count is how you measure that shift.

Our calculator computes true count automatically as you input cards—plus shows exactly how it affects your optimal strategy. See the math in real-time.