Basic Strategy is the foundation of Blackjack, reducing the house edge to roughly 0.5%. But if you want to flip the odds and gain an edge over the casino, Basic Strategy is not enough. You need Deviations.
Deviations (or Index Numbers) are specific moments where the True Count justifies breaking the standard rules. Our **Blackjack Deviations Calculator** replaces static charts with a dynamic tool. It filters the “Illustrious 18” and “Fab 4” indices based on your specific table rules and current count, showing you exactly when to stand on 16 or split Tens.
Blackjack Deviations
Illustrious 18| Player Hand | Dealer Up | Index (TC) | Basic Strategy | Deviation |
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How to Use the Deviations Calculator
This tool is designed to be an interactive reference for card counters practicing their game. It updates in real-time as the shoe heats up.
- Enter Current True Count (TC): Use the plus/minus buttons to input the True Count derived from your running count and deck estimation.
- Tip: Don’t know the True Count? Use our True Count Calculator first.
- Configure Table Rules:
- Surrender (LS): Toggle this “On” to see the “Fab 4” surrender indices. If your casino doesn’t allow Late Surrender, keep it “Off.”
- Dealer Rules: Select whether the dealer Stands on Soft 17 (S17) or Hits Soft 17 (H17). This slightly alters specific indices.
- Manage “Heat”: Check the “Hide High Heat” box if you want to exclude dangerous plays (like Splitting Tens) that alert Pit Bosses to your skill level.
- Read the Chart: The calculator highlights active deviations in green.
- Base: The Basic Strategy move.
- Deviation: The move you should make right now based on the count.
Related Tools: Before applying these aggressive plays, ensure your bankroll can handle the variance using the Risk of Ruin Calculator. To check if a game is worth playing in the first place, use the Penetration Calculator.
Real-World Examples: When to Deviate
Why should you deviate from Basic Strategy? Because as the deck becomes rich in Tens and Aces, the probabilities shift.
Example 1: The “Illustrious 18” #1 Rule (Insurance)
Basic Strategy says never take Insurance. It is a sucker bet.
- Scenario: You have a True Count of +3. The Dealer shows an Ace.
- The Deviation: At TC +3, the probability of the dealer having a Ten in the hole is high enough that Insurance becomes a profitable bet (+EV).
- Action: You buy Insurance.
Example 2: The “Fab 4” Surrender
You have a hard 15 against a Dealer 10. Basic Strategy says to Hit.
- Scenario: The True Count is 0 or higher.
- The Deviation: The Fab 4 index for 15 v 10 is 0. This means if the count is neutral or positive, hitting is suicide.
- Action: Surrender the hand and save half your bet.
Example 3: Standing on 16
You have a hard 16 against a Dealer 10. Basic Strategy says to Hit.
- Scenario: The True Count is positive (any number above 0).
- The Deviation: The deck is rich in high cards. If you hit, you will likely bust. If you stand, there is a higher chance the dealer will bust.
- Action: Stand.
Frequently Asked Questions (FAQ)
What are the “Illustrious 18”?
The Illustrious 18 are the top 18 blackjack deviations defined by Don Schlesinger. While there are hundreds of possible deviations, these 18 offer approximately 90-95% of the total potential gain available from strategy variations. Learning these is essential for any card counter.
What is the “Fab 4”?
The “Fab 4” are the four most important Surrender deviations. If your casino offers Late Surrender, memorizing these four indices is even more valuable than learning the bottom half of the Illustrious 18.
What does “Splitting Tens” mean for Heat?
Mathematically, you should split Tens against a Dealer 5 or 6 if the True Count is very high (+5 or +6). However, this is a glaring signal to casino staff that you are counting cards. Most pros avoid this play to preserve longevity, which is why our calculator has a “Hide High Heat” option.