The Illustrious 18:
Count Deviations That Actually Matter

Basic strategy is the mathematically correct play for every hand in blackjack — assuming a neutral deck. But a card counter knows the deck is never neutral for long. When the true count shifts significantly, certain plays change. These are called index plays or strategy deviations, and the most important 18 of them are known as the Illustrious 18.

What Are Strategy Deviations?

When you count cards, you're tracking the ratio of high cards to low cards remaining in the shoe. When that ratio tilts strongly in your favor — a high true count — the deck is rich in tens and aces. This changes the expected value of certain decisions. Plays that are wrong at a neutral count become correct at a high count, and vice versa.

A strategy deviation is any play where you override basic strategy based on the current true count. The "index" for each deviation is the true count threshold at which the play changes. For example, the Insurance deviation has an index of +3 — meaning you take insurance when the true count is +3 or higher, and decline it at any count below that, regardless of what basic strategy says.

There are hundreds of possible deviations, but the vast majority have such a small expected value impact that they're not worth memorizing. Don Schlesinger's research, published in Blackjack Attack, identified the 18 deviations that account for the overwhelming majority of the edge gained from deviation play. These are the Illustrious 18.

Why They Matter More Than You Think

Many card counters learn the Hi-Lo system, master the true count conversion, and stop there. They vary their bets based on the count — which is the primary source of edge — but they continue to play every hand according to basic strategy. This is leaving money on the table.

Deviation play adds approximately 0.15% to your overall edge, which doesn't sound dramatic until you consider that the total card counting edge over the house is only around 0.5–1.0% to begin with. The Illustrious 18 alone represent roughly 30% of the total edge available from a complete deviation strategy.

The Illustrious 18: Complete List

The following table lists all 18 deviations in order of importance, with the Hi-Lo true count index for each. A positive index means take the action when TC ≥ that number. A negative index means take the action when TC ≤ that number.

The Three You Must Know First

If you're just starting to add deviations to your game, prioritize these three. They appear most frequently and have the highest individual value.

1. Insurance at TC +3

This is the single most valuable deviation in the entire list. Basic strategy says never take insurance — and for a non-counter, that's correct. But when the true count reaches +3, the remaining deck has enough tens in it that insurance becomes a positive expected value bet. At +3, roughly one-third of the remaining cards are tens, which is the threshold at which the insurance side bet breaks even. Above +3, it's profitable.

2. Stand on 16 vs 10 at TC 0 or higher

Basic strategy says hit 16 vs a dealer's 10. But at a neutral or positive count, the deck is rich enough in tens that standing becomes correct. The logic: if the deck is full of tens, you're likely to bust if you hit, and the dealer has a strong chance of already having a pat hand. Standing on 16 vs 10 at TC ≥ 0 is one of the highest-frequency deviations — you'll see 16 vs 10 constantly.

3. Stand on 15 vs 10 at TC +4

Similar logic to 16 vs 10, but requires a stronger count because 15 is a worse starting point. At +4, the bust risk if you hit outweighs the risk of the dealer making their hand. This is a discipline play — every instinct says to hit 15, but the count tells you to stand.

How to Memorize Them Without Losing Your Mind

Trying to memorize all 18 deviations at once is overwhelming and ineffective. The best approach is progressive: master the top 6 first (insurance, 16v10, 15v10, 10,10v5, 10,10v6, 10v10), and only add more once those are automatic. Flashcard drilling — where you see a hand and dealer card and have to name the correct play and index — is the most effective training method.

The key is context: don't just memorize "stand 16 vs 10 at TC 0." Understand why — because a ten-rich deck makes busting on 16 more likely and makes the dealer's hidden 10 more probable. When you understand the logic, the index numbers are much easier to retain.

Using Deviations at a Live Table

The hardest part isn't memorizing the deviations — it's maintaining your count accurately while also recognizing deviation situations as they arise. Your brain has to run two parallel processes: the counting track and the basic strategy + deviation overlay.

This is why deviations should only be added after you can run a full shoe with near-perfect accuracy at pace. Adding them too early leads to errors in both counting and deviation application. The cognitive overhead is real, and rushing it produces sloppy play.

In practice, many counters play with a mental checklist: after every hand, they've already made the count update, assessed the true count, and noted whether the next hand falls into any deviation range. With enough practice, this happens automatically — but it takes hundreds of hours of deliberate drilling to get there.

Beyond the Illustrious 18: The Fab 4

Once you've mastered the Illustrious 18, there's one more set of deviations worth learning: the Fab 4 surrender plays. These are four situations where surrendering becomes the correct play at sufficiently high or low true counts:

• 16 vs 9, surrender at TC ≥ +2 — basic strategy says hit, but the count makes surrender correct
• 16 vs 10, surrender at TC ≥ 0 — the most common Fab 4 situation
• 16 vs A, surrender at TC ≥ +4
• 15 vs 10, surrender at TC ≥ +1

The Fab 4 require late surrender to be available at your table — not all casinos offer it. When they do, these four plays add a small but meaningful edge on top of the Illustrious 18. If your casino doesn't offer surrender, skip these entirely; there's nothing to apply them to.

Together, the Illustrious 18 plus Fab 4 represent the complete deviation library that most professional counters use. Anything beyond this is a form of diminishing returns — the edge gains per additional deviation learned drop off steeply, and the cognitive load increases linearly. Very few players need more than these 22 plays.

The Math Behind Why Deviations Work

Understanding why deviations exist makes them far easier to memorize. Every basic strategy play was derived by calculating expected value across all possible dealer and remaining-deck scenarios at a neutral composition. When the count changes significantly, those expected value calculations shift.

Take insurance as the clearest example. Insurance pays 2:1 if the dealer has blackjack. The break-even point for insurance is when exactly one-third of remaining cards are tens. In a neutral 6-deck shoe, roughly 30.8% of cards are tens — slightly below the break-even threshold, which is why basic strategy says never take insurance. But at TC +3, the deck has been depleted of low cards, and the proportion of remaining tens has risen above one-third. Insurance is now a positive expected value bet. The math has literally changed.

The same logic applies to every deviation. At high counts, the deck is ten-rich, which makes standing on stiff hands more attractive (dealer more likely to bust), doubling more attractive (player more likely to hit a powerful total), and hitting less attractive (player more likely to bust). At low counts, the reverse applies. Every index number represents the exact count at which the expected value of two competing plays crosses over.

Tracking Your Deviation Accuracy

One underappreciated aspect of deviation training is knowing your own error rate. Most counters drill deviations in isolation and assume they're applying them correctly at the table. In reality, the combination of maintaining the count, playing basic strategy, and monitoring for deviation situations creates opportunities for errors that don't appear in practice sessions.

A useful exercise: after drilling each deviation group to apparent mastery, simulate a full shoe while also managing basic strategy decisions and running the count. Pay attention to which deviations you miss or misapply under this combined cognitive load — those are your weak points. Counters who drill deviations in isolation but never combine them with live count practice often discover significant error rates when they actually track their in-session performance.

True Count Trainer Pro's deviation drill mode presents deviations in the context of an active count, simulating the real table condition where you must recognize the situation while already tracking the shoe. This is specifically designed to address the gap between isolated drilling and live application.

The Negative Count Deviations: Often Ignored

Most counters focus on positive-count deviations because that's where they're betting more money. But several of the Illustrious 18 apply at negative counts, and ignoring them leaves edge on the table — even though the amounts bet are smaller.

At low counts (TC −1 or below), the deck is rich in low cards, which changes several plays:

• Stand less on 12–13 vs dealer low cards — the dealer is less likely to bust in a low-card-rich shoe
• Double less aggressively on 10 vs 10 — the player's chance of making a strong total is reduced
• Hit 13 vs 2 and 12 vs 4 and 12 vs 6 at sufficiently negative counts

These plays feel counterintuitive because basic strategy says stand — but at negative counts, you're more likely to pull a low card anyway, and the dealer has improved their chances of reaching a pat hand. The math is clear even when the instinct resists it. This is exactly the kind of situation where trusting the index beats trusting your gut.