Basic strategy is the average optimal play across all possible unseen cards. Counting lets you peek. When the true count tells you the shoe is skewed away from average, specific cells of the chart flip: a hit becomes a stand, a stand becomes a hit, a decline becomes a take. These flips are called deviations, and the top set — Don Schlesinger's Illustrious 18 plus the Fab 4 surrender additions — is where most of your counter EV lives after basic strategy.
This post contains the full tables for 6D S17 DAS LS (standard Vegas Strip), the intuition behind each cell, and how to memorize them without buying a plastic chart.
What a deviation is
A basic-strategy cell has a default action (hit, stand, double, split, surrender). A deviation attaches a true count threshold to that cell:
- "Stand if TC ≥ N": the default is a hit (or surrender); at TC ≥ N you stand instead.
- "Hit if TC ≤ N": the default is a stand; at TC ≤ N you hit.
- "Double if TC ≥ N": at TC ≥ N you double (if the rules allow), otherwise default.
- "Take insurance if TC ≥ N": at TC ≥ N you take the insurance side bet, otherwise decline.
A wrong deviation is worse than no deviation at all. If you mis-apply an index — play the cell as a deviation below its threshold, or fail to deviate above it — you give up more EV than you would have by playing basic. Memorize carefully.
The Illustrious 18
Indices below are for 6-deck, S17, DAS, LS (standard Vegas Strip). Ordered by approximate EV contribution — insurance is by far the most valuable single cell. Source: Schlesinger's Blackjack Attack, cross-referenced against Wizard of Odds and Blackjack Apprenticeship's published I18 charts.
| # | Hand | Dealer | Basic | Deviation | TC Index | |---|---|---|---|---|---| | 1 | Insurance | — | Decline | Take | ≥ +3 | | 2 | 16 | 10 | Hit/Surr | Stand | ≥ 0 | | 3 | 15 | 10 | Hit/Surr | Stand | ≥ +4 | | 4 | 10,10 | 5 | Stand | Split | ≥ +5 | | 5 | 10,10 | 6 | Stand | Split | ≥ +4 | | 6 | Hard 10 | 10 | Hit | Double | ≥ +4 | | 7 | 12 | 3 | Hit | Stand | ≥ +2 | | 8 | 12 | 2 | Hit | Stand | ≥ +3 | | 9 | 11 | A (S17) | Hit | Double | ≥ +1 | | 10 | 9 | 2 | Hit | Double | ≥ +1 | | 11 | Hard 10 | A | Hit | Double | ≥ +4 | | 12 | 9 | 7 | Hit | Double | ≥ +3 | | 13 | 16 | 9 | Hit | Stand | ≥ +4 | | 14 | 13 | 2 | Stand | Hit | ≤ −1 | | 15 | 12 | 4 | Stand | Hit | ≤ 0 | | 16 | 12 | 5 | Stand | Hit | ≤ −2 | | 17 | 12 | 6 | Stand | Hit | ≤ −1 | | 18 | 13 | 3 | Stand | Hit | ≤ −2 |
Why insurance is #1 by a wide margin
Insurance is a side bet offered whenever the dealer shows an Ace. It pays 2:1 on half the original bet if the dealer has a ten in the hole (i.e., a natural blackjack). For a $20 main bet, the insurance wager is $10, and it pays $20 if the dealer has blackjack.
The math. Insurance wins when the dealer's hole card is a ten. The expected value of the bet crosses zero when the probability of a ten equals the payout's inverse — specifically, when ten-valued cards make up more than 1/3 of the remaining shoe.
In a fresh 52-card deck, 16 out of 52 cards are ten-valued (10, J, Q, K — four of each suit). That's 16/52 ≈ 30.8%, just under 1/3. Insurance is a losing bet at neutral count.
As the true count rises, the balance of high vs. low cards shifts toward high cards. By TC = +3, the ten-proportion among unseen cards crosses 1/3, and insurance becomes profitable. Each additional +1 TC above that adds more EV.
Insurance comes up on roughly 1/13 of hands (any time the dealer shows an Ace), and at the thresholds counters encounter, it's one of the highest-frequency profitable side bets in the casino. Taking it correctly accounts for a significant fraction of counter hourly EV.
Important direction check. Insurance is correct at high positive TC (more tens remain). This is the single most miswritten rule in amateur blackjack writing — some posts have the direction backwards. The rule is: more tens unseen → dealer more likely to have a ten in the hole → insurance becomes a favorable bet.
Never take insurance below TC +3. Even TC +2.9 is a losing bet.
The big everyday deviations
16 vs 10 — stand at TC ≥ 0
The single most common deviation. 16 vs 10 is the archetypal stiff hand — basic strategy hits (or surrenders under LS). At TC ≥ 0, the shoe has enough high cards that (a) hitting your 16 busts more, and (b) dealer 10 busts more trying to make 17. The balance tips to standing.
Frequency: the cell comes up several times per shoe. Getting it right generates meaningful EV over hundreds of hands.
12 vs 3 — stand at TC ≥ +2
12 vs 3 is one of the classic basic-strategy "traps" — novices want to stand because "dealer is weak," but basic says hit. At TC ≥ +2, the deviation flips back to stand because the dealer's 3 now busts more often than your 12 finishes safely.
12 vs 2 — stand at TC ≥ +3
Same logic as 12 vs 3, but dealer 2 is slightly stronger than 3 — the threshold is one higher.
15 vs 10 — stand at TC ≥ +4
Rarer because it fires only at high counts, but clean EV when it does. Below +4, basic strategy surrenders (LS) or hits (no LS).
The Fab 4 — late-surrender deviations
Only relevant at late-surrender tables. These four cells swing to surrender at specific TCs, where basic strategy does not surrender:
| # | Hand | Dealer | Deviation | TC Index | |---|---|---|---|---| | 1 | 14 | 10 | Surrender | ≥ +3 | | 2 | 15 | 9 | Surrender | ≥ +2 | | 3 | 15 | A (H17) | Surrender | ≥ +1 | | 4 | 15 | 10 | (already basic — don't un-surrender) | — |
The direction intuition: high counts mean dealer 10s and Aces finish at 20–21 more often, so 14 and 15 lose more than half the time — surrender becomes the better option.
If your table is no-surrender, skip all four. If it's LS, memorize them alongside the I18. Fab 4 #4 is just a reminder not to "un-surrender" 15 vs 10 at lower counts — basic strategy already surrenders it under LS, so there's no index play to make.
How to memorize
Indices cluster around a few magnets: 0, ±2, ±4, and the insurance +3. If you learn the clusters and remember which hands fall in each, you've covered most of the chart without rote grid memorization.
A practical order to master:
- Insurance +3. The highest-EV single cell. Drill until you can't get it wrong.
- 16 vs 10 at 0. The most frequent deviation. Comes up roughly once per shoe.
- 12 vs 2 and 12 vs 3. Common stiff-vs-weak-upcard cells with adjacent indices (+3 and +2).
- 15 vs 10 at +4. The next-most-common "high-count stand."
- The rest of the I18. Doubles on 10/11, split 10s at very high counts, the negative-TC hits.
- Fab 4. Only if your table has LS.
Why H17 and single-deck charts differ
Indices shift under different rule sets:
- H17 (dealer hits soft 17): 11 vs A basic is already double, so I18 #9 doesn't apply. Some other cells shift by ±1. 15 vs A Fab 4 is specifically an H17 cell — under S17 it's covered by basic strategy.
- Single-deck / double-deck: an entirely different (and larger) deviation chart applies. The 6D S17 I18 is a solid starting point but not complete for 1D/2D play. Serious 1D players use a ~25-cell chart specific to single-deck.
- No LS: the Fab 4 becomes irrelevant; their basic equivalents are all hits.
For most 6D S17 DAS LS tables in Las Vegas and most regional US markets, the I18 plus Fab 4 above is the canonical set. Verify against Wizard of Odds or Schlesinger before relying on anything.
The drill
Our deviations training module runs 35 scenarios across the full I18 + Fab 4 + mixed basic-vs-deviation cases. Each wrong answer triggers a 30-second review explaining the math. 9/10 unlocks the next module; 10/10 earns a badge.
Ready to see where you stand? Take the 15-hand test — 15 real hands scored on counting, true-count conversion, and action decisions.