Blackjack Deviations — Index Plays & the Illustrious 18

Deviations (or index plays) are the points where the count tells you to override basic strategy. Basic strategy is correct for an average shoe; once you are counting, the composition has changed, and a handful of plays flip. The most valuable set is the Illustrious 18.

How an index play works

Every deviation has an index number — the true count at which the better action switches. Below the index you play basic strategy; at or above it you deviate. For example, 16 vs 10 is normally a hit (or surrender), but it becomes a stand at true count 0 or higher — the shoe is ten-rich enough that drawing busts you too often.

The highest-value deviations

A few index plays earn most of the money, because they come up often and the EV swing is large (S17, 6-deck indices shown):

• Insurance — take it at true count +3 or higher. The single most valuable deviation; see why insurance is normally a trap.
• 16 vs 10 — stand at 0+.
• 15 vs 10 — stand at +4.
• 10,10 vs 5 or 6 — split at +5.
• 12 vs 3 — stand at +2; 12 vs 2 — stand at +3.
• 11 vs A — double at +1. 9 vs 2 — double at +1. 10 vs 10 — double at +4.

H17 games shift a few indices, and the full Illustrious 18 plus the Fab 4 surrender indices extend the list. Memorizing them is the classic counter's homework.

Skip the index tables — read the crossover directly

An index number is just the true count where one action's EV passes another's. Fullcount computes both EVs exactly from the cards remaining, so instead of recalling "16 vs 10 stand at 0," you can deal out the shoe and watch the best action change the moment it actually does:

Deviations only pay off once you are already counting — start with Hi-Lo and converting to the true count, then size your bets with a bet spread.