Advanced strategy with discipline

Blackjack deviations chart: 16 vs 10 index and True Count

Index numbers, Illustrious 18 context, Hi-Lo triggers, and Hi-Opt I/II caveats for advanced decisions that should not be guessed.

May 9, 2026BJCPRO editorial team7 min read

Basic strategy is the floor. A blackjack deviations chart lists the small set of plays where the True Count says the remaining shoe is different enough to change the default decision, including common searches such as 16 vs 10 index.

See deviations chart Practice a hand

Direct answer

What are blackjack deviations?

A deviation is a planned departure from basic strategy when the count reaches a known index number. You are not ignoring basic strategy; you are using the count to decide when the composition of the remaining cards has changed enough to justify a different play.

Before memorizing

Three conditions must be true

Deviations only make sense after your baseline is stable. If the basic-strategy decision is still shaky, adding indices usually creates more errors than value.

  • You know the basic-strategy chart for the table rules you are studying.
  • Your running count and True Count conversion are automatic enough under pressure.
  • You train each deviation as a specific hand, dealer card, index, and action.

Reference indices

Common Hi-Lo deviations worth training first

These examples show how index numbers work in practice. Treat them as a training map, not as a universal casino prescription: S17/H17, DAS, surrender, deck count, Hi-Lo versus Hi-Opt tags, and the exact index set can change the number.

Read every row the same way: at the index or above, take the play shown; below it, follow basic strategy. The values are for Hi-Lo in a six-deck shoe with the dealer standing on soft 17.

SituationTriggerPlayWhy it changes
Hard 16 vs dealer 10TC 0+Stand instead of hit

A neutral or positive shoe makes drawing into a bust less attractive than letting the dealer act.

Insurance vs dealer AceTC +3Take insurance only at the index

The side bet needs a high density of ten-value cards to be defensible.

Hard 15 vs dealer 10TC +4Stand instead of hit

At a high count, the extra tens make hitting a stiff hand more punishing.

Hard 10 vs dealer 10TC +4Double when allowed

The remaining shoe is rich enough in strong cards to make the aggressive play worth studying.

Hard 12 vs dealer 3TC +2Stand instead of hit

More high cards increase the risk of busting while the dealer still has pressure.

Hard 12 vs dealer 2TC +3Stand instead of hit

The index waits for a stronger signal because the dealer 2 is less vulnerable than a weak upcard like 5 or 6.

Pair of tens vs dealer 5TC +5Split

Only a very ten-rich shoe justifies breaking a made 20.

Pair of tens vs dealer 6TC +4Split

Same logic as against a 5, with a slightly higher dealer bust rate.

Hard 11 vs dealer AceTC +1Double when allowed

A barely positive shoe already makes doubling better than hitting.

Hard 10 vs dealer AceTC +4Double when allowed

Needs a much richer shoe than 11 vs Ace, because the ace hurts more.

Hard 9 vs dealer 2TC +1Double when allowed

A small positive edge is enough to tip this borderline double.

Hard 9 vs dealer 7TC +3Double when allowed

The dealer 7 is strong, so it takes more tens to justify doubling.

Hard 16 vs dealer 9TC +5Stand

Standing only pays once the shoe is clearly loaded with tens.

Hard 12 vs dealer 4TC 0Stand

The classic borderline hand: it flips right at neutral.

Hard 13 vs dealer 2TC -1Stand

Below the index the shoe is small-card rich and hitting becomes the better play.

Hard 13 vs dealer 3TC -2Stand

Same idea as 13 vs 2, but it takes a clearly negative shoe.

Hard 12 vs dealer 5TC -2Stand

Holds as a stand until the shoe turns clearly negative.

Hard 12 vs dealer 6TC -1Stand

The dealer 6 busts often, so standing holds until slightly negative.

If your table allows late surrender, keep a separate surrender chart. If you searched for a Hi-Opt I 16 vs 10 index or Hi-Opt II 16 vs 10 index, do not copy the Hi-Lo trigger blindly; use the index chart for that system and rule set.

Beyond the table

Why an index is an approximation, and what replaces it

An index compresses the entire shoe into a single number. That compression exists for a human reason: at a live table nobody can compute expected value card by card, so the shoe is reduced to a true count and the point where a decision flips is memorised.

The BJCPRO counter does not work that way. Its Monte Carlo engine receives the exact composition of the remaining shoe, how many aces, how many tens, how many of each rank, and simulates from it. It never receives a running count or a true count, because it does not need the summary: it already has what the summary approximates. That is also why it adjusts on its own to H17 or S17 and to the number of decks, which are exactly the conditions that move an index.

It is also why you will not find Hi-Opt I, Hi-Opt II or Zen index tables published here. Those tables belong to their authors, and even QFIT, the reference software in this field, declines to publish them for copyright reasons. What changes from one system to another is the tag set, and with it its betting correlation, playing efficiency and insurance correlation.

Try it here

Calculate the play from the real shoe, not from an index

Set the hand, the dealer up card and how many cards of each rank are still in the shoe. The engine simulates from that exact composition and returns the expected value of every legal decision. Notice that it never asks you for a running count.

Start from:

Your total: 16

The table above assumes six decks, S17 and no surrender. Change a rule and the best play can change with it.

Cards still in the shoe

A
24
2
24
3
24
4
24
5
24
6
23
7
24
8
24
9
24
10
94
Cards left: 309 Hi-Lo running count: -1 True count: -0.2
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The running count and true count above are shown only so you can compare. The engine never receives them: it reads the composition directly, which is why two shoes with the same true count can return different plays.

Open the counter See the expected value of each decision from the real shoe, with no index to memorise.

Practice path

Train one deviation at a time on the real table flow

Open a hand, say the basic-strategy play first, then add the index condition out loud: “I stand only when the True Count is at or above the trigger.” This keeps the deviation tied to the decision, not to memorized trivia.

Hard 16 vs dealer 10The first stiff-hand deviation most players should make automatic.Hard 15 vs dealer 10A higher-count decision that punishes rushed counting.Hard 12 vs dealer 3Useful for learning why the same total changes by dealer upcard.Hard 10 vs dealer 10A clean example of when positive count can justify aggression.

FAQ

Common questions before learning deviations

Is the Hi-Opt II 16 vs 10 index the same as Hi-Lo?

Not necessarily. Hi-Lo, Hi-Opt I, and Hi-Opt II use different tag structures, and the exact index can also depend on rules, decks, surrender, and side-count assumptions. Learn the decision logic here, then train the chart that belongs to your system.

Are deviations more important than basic strategy?

No. Basic strategy is the base of every decision. Deviations are a smaller advanced layer used only when the count reaches a defined index.

Do all counting systems use the same index numbers?

No. Hi-Lo, KO, Zen, Wong Halves, and other systems can use different references. Train the chart that belongs to your system and rules.

Should I memorize every deviation at once?

No. Start with the highest-value plays, especially insurance and the most common stiff-hand decisions, then expand only after accuracy stays stable.

Do deviations guarantee profit?

No. They reduce decision error in specific count conditions, but variance, rules, penetration, bankroll, and execution still matter.

Responsible training

Use deviations as study tools, not promises

This guide is for blackjack education and practice. It does not guarantee results, remove variance, or recommend betting beyond a disciplined bankroll plan.