Every counting student eventually discovers an uncomfortable fact: complete index tables list well over a hundred spots where the count can flip the correct play, and memorizing all of them is a monstrous job with feeble returns. Don Schlesinger's contribution, in his book Blackjack Attack, was to rank the deviations by how much each is actually worth and publish the honest conclusion: eighteen of them deliver the large majority of the available playing gain. The list has been called the Illustrious 18 ever since, and it turned deviation study from a memorization swamp into a short, ordered curriculum.
What a deviation actually is
Basic strategy is the perfect answer to an average shoe. But a counter, by definition, knows when the shoe is not average: a high true count means the remaining cards are unusually ten-rich, and that changes the physics of a handful of decisions. Standing on 16 against a 10 is wrong in a neutral shoe, but when tens are thick, the hit busts more often and the dealer's forced draws break more often too; at some point the balance tips and standing becomes right.
That tipping point is the index. Each Illustrious 18 entry is a hand, an upcard, and the true count at which the play flips. Below the index you play basic strategy; at or above it, you deviate. Nothing mystical happens: the arithmetic that produced the chart is simply being rerun with the shoe you actually face.
The famous entries
The canonical numbers below are from Schlesinger's published multi-deck, dealer-stands-on-soft-17 list, in Hi-Lo true counts; treat them as the reference shape and verify the exact values for your rules before studying seriously.
- Insurance at +3. The most valuable deviation by a wide margin, and the whole list's poster child. Basic strategy never insures; a ten-rich shoe makes the dealer's blackjack frequent enough that the 2:1 side bet turns profitable. It ranks first because the spot recurs every time an ace shows.
- Stand 16 vs 10 at 0 or higher. The most used hand deviation: any positive count flips the game's most notorious decision from hit to stand.
- Stand 15 vs 10 at +4. The 16's little sibling, needing a richer shoe to tip.
- Split 10s vs 5 at +5 and vs 6 at +4. The infamous one: breaking a made 20 becomes mathematically right when tens are dense enough that each new hand expects to catch one. Correct, conspicuous, and famously the play that draws the pit's attention.
- Double 10 vs 10 at +4, double 11 vs A at +1, double 9 vs 2 at +1. Aggressive doubles that a rich shoe unlocks, extending the ladder from our doubling guide.
- Stand 12 vs 3 at +2, stand 12 vs 2 at +3. The stiff-hand borderlands, where modest counts push marginal hits to stands.
- Negative-count entries such as hitting 13 against a 2 or 3 when the count falls below the index: thin shoes turn cautious stands back into hits, a reminder the list runs in both directions.
A companion set, the Fab 4, covers the most valuable late-surrender indices (15 and 14 against strong upcards); it belongs to the same family and the same book, and most players learn it immediately after the 18.
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Where deviations rank in the skill stack
Honesty requires proportions: bet variation, not play variation, is the engine of counting. Scaling bets with the count produces the clear majority of a counter's edge; the entire Illustrious 18 adds a meaningful but distinctly smaller layer on top, per the published analyses. That ordering dictates the curriculum from our counting overview: automatic basic strategy, then a flawless count, then the bet spread, and only then indices. A deviation executed off a wobbly count is worse than no deviation at all, because you pay its cost in errors without collecting its premium.
The same proportions explain who should bother. A recreational counter practicing for the intellectual sport gets most of the fun from insurance plus the first few entries; the full eighteen is for players pursuing the last increments of theoretical edge. Both are legitimate ways to enjoy the skill; only one requires flashcards in your pocket for a month.
Learning them for real
The list is short, but table execution is a recognition task under load: the count sits at +4, a 15 lands against a 10, and the flip has to fire in the second you have. Study order follows value: insurance first, then 16 vs 10, then down the ranking. Drill each index in isolation until the trigger is reflexive, then mixed, then inside full-speed play with the count running, which is exactly the progression a dedicated deviation trainer automates. And keep the frame the callout above insists on: indices are the graduate seminar of a skill whose every level, per the honest limits in our counting overview, offers a thin edge, thick variance, and casinos entitled to refuse the game. The Illustrious 18 is applied probability at its most elegant; learn it because the machinery is beautiful, and let that be the payoff.
Frequently asked questions
What is the Illustrious 18 in blackjack?
It is Don Schlesinger's ranked list, published in Blackjack Attack, of the eighteen count-based strategy deviations that deliver the large majority of the playing gain available to a card counter. Each entry names a hand, a dealer upcard, and an index: the true count at which the correct play flips from the basic strategy answer to an alternative.
What is an index play or deviation?
A deviation is a spot where the count overrides basic strategy. Basic strategy assumes an average deck, but a strong count means the remaining shoe is unusually rich or poor in high cards, and for a small set of hands that changes the best action. The index is the trigger: reach that true count and you switch plays; below it, basic strategy stands.
What is the most important deviation to learn first?
Insurance, at a Hi-Lo true count of about +3, per Schlesinger's published list. Basic strategy refuses insurance always, but a ten-rich shoe pushes the dealer's blackjack odds past the break-even point, making the side bet profitable. It tops the ranking because the situation arises every time the dealer shows an ace, far more often than any single hand combination.
Do deviations matter more than bet spreading?
No. Varying bets with the count produces the clear majority of a counter's total edge; the full Illustrious 18 adds a meaningful but smaller slice on top. That is why the learning order is fixed: automatic basic strategy first, then an accurate count, then bet spreading, and only then deviations. Indices layered onto a shaky count subtract value rather than add it.
Are the Illustrious 18 index numbers the same at every table?
No. The canonical numbers were computed for multi-deck games with the dealer standing on soft 17, and they shift with rules, deck count, and the counting system in use; H17 games and single-deck games use somewhat different values, and unbalanced counts like KO use their own. Learn indices from a source computed for your rules and system, and verify against the published lists.