Basic Strategy Counting Systems Deviations Reference

Strategy Deviations Reference

Once you can keep a perfect running count and convert to true count, the next step is learning when to deviate from basic strategy. The Illustrious 18 and Fab 4 are the most valuable deviations for the Hi-Lo counting system in a 6-deck S17 DAS game.

How Deviations Work

Positive Index Numbers

When the index is positive (e.g. +3), deviate from basic strategy when the true count is at or above that number. For example, Insurance at +3 means: take insurance when TC is +3 or higher.

Negative Index Numbers

When the index is negative (e.g. -1), deviate from basic strategy when the true count is at or below that number. For example, 13 vs 2 at -1 means: hit instead of stand when TC is -1 or lower.

The Illustrious 18

The 18 most valuable count-dependent strategy deviations, ordered by importance. The first 6 provide roughly 90% of all deviation value.

#	Play	Idx	Dev	Basic	Explanation
1	Any vs A	+3	Insurance	Hit	Take insurance when true count is +3 or higher. This is the single most valuable deviation, accounting for ~25% of all deviation value.
2	16 vs 10	+0	Stand	Hit	Stand on 16 vs dealer 10 when the true count is 0 or higher. Basic strategy says hit, but at TC 0+ the extra 10s in the deck make standing correct.
3	15 vs 10	+4	Stand	Hit	Stand on 15 vs dealer 10 when true count is +4 or higher. The high count means more 10s remain, making hitting riskier.
4	10,10 vs 5	+5	Split	Stand	Split 10s vs dealer 5 when true count is +5 or higher. Extremely aggressive play that exploits a very dealer-unfavorable situation.
5	10,10 vs 6	+4	Split	Stand	Split 10s vs dealer 6 when true count is +4 or higher. The dealer's weakest upcard combined with a rich deck makes splitting profitable.
6	10 vs 10	+4	Double Down	Hit	Double down on 10 vs dealer 10 when true count is +4 or higher. A 10-rich deck gives strong chances of drawing to 20.
7	12 vs 3	+2	Stand	Hit	Stand on 12 vs dealer 3 when true count is +2 or higher. The extra 10s make busting more likely if you hit.
8	12 vs 2	+3	Stand	Hit	Stand on 12 vs dealer 2 when true count is +3 or higher. Similar logic to 12 vs 3 but requires a slightly higher count.
9	11 vs A	+1	Double Down	Hit	Double down on 11 vs Ace when true count is +1 or higher. In S17 games, basic strategy says hit, but a positive count makes doubling correct.
10	9 vs 2	+1	Double Down	Hit	Double down on 9 vs dealer 2 when true count is +1 or higher. A slightly positive deck makes this borderline hand worth doubling.
11	10 vs A	+4	Double Down	Hit	Double on 10 vs Ace when true count is +4 or higher. Requires a significantly rich deck to overcome the dealer's strong upcard.
12	9 vs 7	+3	Double Down	Hit	Double on 9 vs dealer 7 when true count is +3 or higher. The dealer's 7 is less dangerous than 8+, and a rich deck favors doubling.
13	16 vs 9	+5	Stand	Hit	Stand on 16 vs dealer 9 when true count is +5 or higher. This requires a very high count where busting risk outweighs the benefit of hitting.
14	13 vs 2	-1	Hit	Stand	Hit 13 vs dealer 2 when true count is -1 or lower. Basic strategy says stand, but a negative count means fewer 10s and hitting becomes correct.
15	12 vs 4	+0	Hit	Stand	Hit 12 vs dealer 4 when true count is 0 or lower. At a neutral or negative count, hitting 12 against the dealer's 4 is more profitable.
16	12 vs 5	-2	Hit	Stand	Hit 12 vs dealer 5 when true count is -2 or lower. In a very negative count, the deck is small-card-heavy and standing becomes a losing play.
17	12 vs 6	-1	Hit	Stand	Hit 12 vs dealer 6 when true count is -1 or lower. Even against the dealer's worst upcard, a sufficiently negative count tips the scale.
18	13 vs 3	-2	Hit	Stand	Hit 13 vs dealer 3 when true count is -2 or lower. A depleted deck of 10s means standing is no longer the best play.

The Fab 4

Four surrender deviations that apply when late surrender is available.

#	Play	Idx	Action	Explanation
1	14 vs 10	+3	Surrender	Surrender 14 vs dealer 10 when true count is +3 or higher. Not a basic strategy surrender, but becomes correct in a 10-rich deck.
2	15 vs 10	+0	Surrender	Surrender 15 vs dealer 10 at true count 0 or higher. This is already a basic strategy surrender in many rule sets, but the index confirms it.
3	15 vs 9	+2	Surrender	Surrender 15 vs dealer 9 when true count is +2 or higher. The 9 combined with a high count makes this hand hopeless.
4	15 vs A	+2	Surrender	Surrender 15 vs dealer Ace when true count is +2 or higher. The dealer's ace with a rich deck makes both hitting and standing unattractive.

Learning Tips

Start with the top 6. Insurance, 16v10, 15v10, 10,10v5, 10,10v6, and 10v10 account for ~90% of all deviation value.
Memorize the index numbers. Create flashcards: "16 vs 10 = 0", "Insurance = +3", etc.
Practice with context. Use the deviation drill to see hands with true counts and make the right decision under pressure.
Remember the direction. Positive indices mean the deviation kicks in at high counts (more 10s). Negative indices kick in at low counts.

Practice Deviations