Hi-Lo Deviations

When to break from basic strategy based on the count

What are Deviations?

Basic strategy assumes you have no knowledge of remaining cards. But when counting, you know if the deck is rich or poor in certain cards. Deviations are adjusted plays that become mathematically correct at specific true counts.

Positive Index (+)

Deviate when true count is at or above the index. High counts mean more 10s/Aces remain.

Negative Index (-)

Deviate when true count is at or below the index. Low counts mean more small cards remain.

The Illustrious 18

Show descriptions

#1Insurance

Hit→Stand

Take insurance when true count is +3 or higher

#216 vs 10

Hit→Stand

Stand on 16 vs 10 when true count is 0 or higher

#315 vs 10

Hit→Stand

Stand on 15 vs 10 when true count is +4 or higher

#410,10 vs 5

Stand→Split

Split 10s vs 5 when true count is +5 or higher

#510,10 vs 6

Stand→Split

Split 10s vs 6 when true count is +4 or higher

#610 vs 10

Hit→Double

Double 10 vs 10 when true count is +4 or higher

#712 vs 3

Hit→Stand

Stand on 12 vs 3 when true count is +2 or higher

#812 vs 2

Hit→Stand

Stand on 12 vs 2 when true count is +3 or higher

#911 vs A

Hit→Double

Double 11 vs Ace when true count is +1 or higher

#109 vs 2

Hit→Double

Double 9 vs 2 when true count is +1 or higher

#1110 vs A

Hit→Double

Double 10 vs Ace when true count is +4 or higher

#129 vs 7

Hit→Double

Double 9 vs 7 when true count is +3 or higher

#1316 vs 9

Hit→Stand

Stand on 16 vs 9 when true count is +5 or higher

#1413 vs 2

-1

Stand→Hit

Hit 13 vs 2 when true count is -1 or lower

#1512 vs 4

Stand→Hit

Hit 12 vs 4 when true count is 0 or lower

#1612 vs 5

-2

Stand→Hit

Hit 12 vs 5 when true count is -2 or lower

#1712 vs 6

-1

Stand→Hit

Hit 12 vs 6 when true count is -1 or lower

#1813 vs 3

-2

Stand→Hit

Hit 13 vs 3 when true count is -2 or lower

Quick Reference Table

#	Hand	Index	Basic	Deviation
1	Insurance	+3	H	S
2	16 vs 10	+0	H	S
3	15 vs 10	+4	H	S
4	10,10 vs 5	+5	S	P
5	10,10 vs 6	+4	S	P
6	10 vs 10	+4	H	D
7	12 vs 3	+2	H	S
8	12 vs 2	+3	H	S
9	11 vs A	+1	H	D
10	9 vs 2	+1	H	D
11	10 vs A	+4	H	D
12	9 vs 7	+3	H	D
13	16 vs 9	+5	H	S
14	13 vs 2	-1	S	H
15	12 vs 4	+0	S	H
16	12 vs 5	-2	S	H
17	12 vs 6	-1	S	H
18	13 vs 3	-2	S	H
19	14 vs 10	+3	H	R
20	15 vs 10	+0	H	R
21	15 vs 9	+2	H	R
22	15 vs A	+1	H	R

Key Takeaways

Insurance is #1

The most valuable deviation is taking insurance at TC +3 or higher. Basic strategy says never take it, but with a rich deck it becomes profitable.

16 vs 10 is Close

The famous 16 vs 10 is a deviation at TC 0 - almost a coin flip at basic strategy. Any positive count tips the scales toward standing.

Learn by Priority

The Illustrious 18 are ordered by value. Focus on mastering #1-6 before learning the rest. 90% of the value comes from the first few deviations.

Memorization Tips

1.Group by pattern: Notice that 12 vs 2-6 all have negative indices (hit when deck is poor).
2.Use rhymes: “Insurance at three” - take insurance at TC +3.
3.Practice scenarios: Deal yourself hands and quiz yourself on the deviation indices.
4.Understand the logic: High count = more 10s, so stand more often (dealer busts more) and double more aggressively.

Practice with Counting Review Counting Systems