An index play is a hand where a high enough count makes the chart wrong. There are 22 of them worth knowing. Between them they capture 80 to 85% of everything a counter can gain from deviating from basic strategy at all — which is why nobody learns the other few hundred.
These numbers are for one specific game: dealer stands on soft 17, double after split, late surrender, blackjack pays 3:2, dealt from four to eight decks (6 by default). A strategy chart is only correct for the ruleset it was computed for — what changes when the rules change.
The Illustrious 18 are Don Schlesinger’s eighteen most valuable playing deviations, from Blackjack Attack. The Fab 4 are the four most valuable late-surrender indices. Insurance sits alongside them: it is not a hand decision at all but a side bet, and at a high enough count it is the single most profitable deviation there is.
Every number below is a true count, not a running count. Read a row as: at or above this count, make the play in the third column; below it, do what the fourth column says.
| Index | At or above | Below | |
|---|---|---|---|
| Insurance | TC ≥ +3 | Take insurance | Never take it |
| 16 vs 10 | TC ≥ 0 | Stand | Hit |
| 15 vs 10 | TC ≥ +4 | Stand | Surrender (basic strategy) |
| 10,10 vs 5 | TC ≥ +5 | Split | Stand (basic strategy) |
| 10,10 vs 6 | TC ≥ +4 | Split | Stand (basic strategy) |
| 10 vs 10 | TC ≥ +4 | Double | Hit (basic strategy) |
| 12 vs 3 | TC ≥ +2 | Stand | Hit (basic strategy) |
| 12 vs 2 | TC ≥ +3 | Stand | Hit (basic strategy) |
| 11 vs A | TC ≥ +1 | Double | Hit (basic strategy) |
| 9 vs 2 | TC ≥ +1 | Double | Hit (basic strategy) |
| 10 vs A | TC ≥ +4 | Double | Hit (basic strategy) |
| 9 vs 7 | TC ≥ +3 | Double | Hit (basic strategy) |
| 16 vs 9 | TC ≥ +5 | Stand | Surrender (basic strategy) |
| 13 vs 2 | TC ≥ −1 | Stand | Hit |
| 12 vs 4 | TC ≥ 0 | Stand | Hit |
| 12 vs 5 | TC ≥ −2 | Stand | Hit |
| 12 vs 6 | TC ≥ −1 | Stand | Hit |
| 13 vs 3 | TC ≥ −2 | Stand | Hit |
| 14 vs 10 | TC ≥ +3 | Surrender | Hit (basic strategy) |
| 15 vs 10 (surrender) | TC ≥ 0 | Surrender | Hit |
| 15 vs 9 | TC ≥ +2 | Surrender | Hit (basic strategy) |
| 15 vs A | TC ≥ +1 | Surrender | Hit (basic strategy) |
Most indices are positive: the deviation switches on when the shoe goes rich. A few are zero or negative, and those work the other way round — the play at or above the index is basic strategy, and what the index buys you is knowing when to abandon it in a poor shoe. Standing on 13 against a 2 is ordinary; hitting it at a true count of −2 is the deviation.
Two rows cover the same hand. 15 against a ten is both an Illustrious 18 stand and a Fab 4 surrender, and when both apply the surrender wins, because it is the better of the two.
Insurance is a bet that the dealer’s hole card is a ten, paying 2:1. Roughly four cards in thirteen are tens, so it is a losing bet in a neutral shoe and basic strategy says never take it. But it is a bet purely about the density of tens left — which is exactly what the count measures. At a true count of +3 or better, tens are dense enough that the bet turns positive.
This is also why “even money” on a blackjack is the same decision wearing a disguise: it is insurance on a hand you were going to win anyway. Below the index, decline it.
Insurance, then 16 against a ten, then 15 against a ten. Those three carry a disproportionate share of the value: insurance because the bet is large and the edge is clean, and the two stiffs because they come up constantly. After that, the rest of the stands, then the doubles, then the surrenders.
Drill the index plays Flashcards that hand you a count and ask for the play. Missed cards come back sooner.
These indices are derived for a multi-deck game where the dealer stands on soft 17. Under H17 several of them shift, particularly the ones against a dealer ace, because H17 changes basic strategy itself — 11 against an ace and 15 against an ace become near-basic plays, so their indices move toward zero or drop out altogether. The count-neutral stiffs and insurance are essentially unchanged.
The trainer will not apply this table to an H17 game. It disables deviations and says why, rather than quietly using S17 numbers on the wrong ruleset — see where the numbers come from.
The eighteen most valuable basic-strategy deviations for a Hi-Lo card counter, identified by Don Schlesinger in Blackjack Attack. Each one is a hand where, above a specific true count, the correct play differs from the basic strategy chart.
The four most valuable late-surrender index plays: 14 against a ten, 15 against a ten, 15 against a nine and 15 against an ace. They only apply at tables that offer surrender.
At a true count of plus 3 or higher. Below that, insurance is a losing bet and basic strategy correctly says to decline it. Taking even money on a blackjack is the same bet and follows the same rule.
No. Most of a counter edge comes from bet sizing rather than from deviations. Insurance, 16 against a ten and 15 against a ten carry a large share of the deviation value on their own, and are a reasonable place to stop if you are learning.