The Illustrious 18: count-based plays worth learning first

Basic strategy is the best fixed answer for a fresh shoe. Once you are tracking a Hi-Lo true count, a few of those answers turn out to be close calls that tip the other way when the shoe is rich or poor in tens. Don Schlesinger, in Blackjack Attack, ranked the changes by how much each is worth and published the top eighteen as the Illustrious 18. The numbers below are his Hi-Lo indices for multi-deck games where the dealer stands on soft 17.

What an index is

An index is a true count. It is the point at which the second-best play overtakes the one in basic strategy. The rule has two forms:

• For a positive or zero index on a play that basic strategy does not make, make it when the true count is at or above the index.
• For the plays where basic strategy stands and the index is the reverse, hit when the true count is below the index. At the index itself, stay with basic strategy.

A worked case. The running count is +9 with two decks left, so the true count is 9 ÷ 2 = +4.5. You hold 15 against a dealer 10. Basic strategy hits, but the index for standing is +4, and 4.5 is above it, so you stand. Now take 12 against a 5 with a running count of −3 and a deck and a half left: −3 ÷ 1.5 = −2. The index is −2 and the count is not below it, so you stand as usual. At −8 with two decks left the true count is −4, which is below −2, and you hit.

The eighteen plays

"10,10" is a pair of ten-value cards. Where late surrender is offered, basic strategy gives up 16 against 9, 10 and ace and 15 against 10 before any of those stands apply, and surrender has its own separate indices. The late surrender post covers the four basic-strategy surrenders.

Why these hands

Look at the pattern. Five of the plays are stands on stiff hands: 16 and 15 against a 10, 16 against a 9, 12 against a 2 or 3. These hands lose a lot either way, and what decides between hitting and standing is how likely the next card is to bust you. Hitting a 16 busts on any 6 or higher, and in a ten-rich shoe that is more likely, which is why 16 against 10 flips at 0 and 16 against 9, a slightly better dealer card for you, needs +5.

The doubles and splits work the same way in reverse. Doubling 10 or 11 wants a big card, and a high true count means more of them. Splitting tens breaks up a strong 20, so it only pays when the shoe is very rich in tens. That is why 10,10 against 5 needs +5 and against 6 needs +4, and it is why never splitting tens is the right rule at a true count below those numbers.

The five negative-side plays are the opposite: basic strategy stands on 12 or 13 against a weak dealer card because the dealer is likely to bust. When the shoe is poor in tens the dealer busts less often and your own draw is safer, so hitting takes over.

How to learn them

1. Start with insurance and 16 against 10. Insurance at +3 is the most clear-cut because it depends only on the share of tens, as the insurance post shows: it breaks even once a third of the unseen cards are tens. The 16 against 10 stand at 0 applies whenever the count is neutral or better.
2. Learn the zero and ±1 indices next: 12 against 4, 11 against ace, 9 against 2, 13 against 2 and 12 against 6. The true count spends much of its time near zero, so these apply often.
3. Leave the +5 plays for last. A true count of +5 is rare, so 16 against 9 and 10,10 against 5 matter least in practice.

Two cautions. First, the indices are tied to their rule set: a different number of decks or a dealer who hits soft 17 shifts some of them, so use the table only for the stated game. Second, the published numbers assume a particular rounding convention for the true count, so check how your source rounds before you compare.

Blackjack Coach: Learn 21 covers basic strategy, insurance and Hi-Lo card counting. Basic strategy is the baseline these indices adjust, so be fluent in it first.