Blackjack Deviations Trainer
Drill the Illustrious 18 and Fab 4 — the playing and surrender decisions that change with the count. You get a hand, the dealer upcard, and a true count, and you make the call. Hi-Lo indices, graded against a verified engine.
Index values are calculated for Hi-Lo, the system almost everyone uses for deviations. New here? Start with the Top 6 — they carry most of the value.
How the Deviations Trainer works
The Deviations Trainer is a free, in-browser drill for the most valuable count-based playing decisions in blackjack: the Illustrious 18 and the Fab 4. A deviation is a hand you play differently from basic strategy once the count is high or low enough — for example, you normally hit 16 against a dealer 10, but at a true count of 0 or higher you stand instead. Each deviation has an index number: the true count at which the better play flips.
The trainer shows you a hand, the dealer's upcard, and the current true count, then asks for the correct play. Every answer is graded against the same verified engine behind our other tools, using the standard Hi-Lo index values — the numbers the large majority of counters actually use. It runs entirely on your device; nothing is saved or sent.
How to use it, step by step
- Make sure basic strategy is automatic first. Deviations are exceptions to basic strategy, so the baseline has to be reflexive before the exceptions mean anything. If you are not there yet, spend time in the Basic Strategy Trainer, then come back.
- Choose which deviations to drill. Use the Which deviations? control: Both, the Illustrious 18 only, the Fab 4 only, or the Top 6. New here? Start with Top 6 — those six, led by taking insurance at +3, carry the large majority of the value of all the indices combined.
- Read the situation. Each hand shows the dealer's upcard, your cards, and a true count badge. That true count is the key — it decides whether the count-based play or the basic-strategy play is correct right now.
- Make the call. You get exactly two choices — the index's count-based play and its basic-strategy fallback. Pick the one that is right at the true count shown.
- Read the feedback. The trainer tells you the correct play and states the rule in plain English — the index number and what to do above and below it. That is the part you are actually memorizing, so do not skip it.
- Widen as you improve. Get the Top 6 near-perfect, then switch to the full Illustrious 18, then add the Fab 4 surrenders. Your streak and accuracy track each session.
Every feature, explained
- Four practice sets: Both, Illustrious 18, Fab 4, and Top 6 — so you can isolate the highest-value plays first or drill the whole list.
- Realistic prompts: a real dealer upcard, a real hand, and a true count, exactly as you would face the decision at the table.
- Clean two-choice answers. Every prompt is the count-based play versus its fallback — never a long menu of buttons. That keeps the focus on the one thing that matters (does the count change the play?) and avoids offering plays that would be illegal for the hand.
- Plain-English rule feedback after every answer, including the exact index and the insurance threshold of +3, so each rep reinforces the actual number.
- Hi-Lo index values throughout, graded by a verified engine — because the Illustrious 18 and Fab 4 indices are calculated for Hi-Lo specifically.
- Live streak, accuracy, and best-streak tracking so you can see which sets you have locked in and which need more reps.
Want the full reference — every index, every rule, ranked by value? It lives on our Illustrious 18 & Fab 4 chart, with a deeper write-up in Deviations & Index Plays. Still building the count itself? Drill it in the Card Counting Trainer.
Frequently asked questions
What counters ask before drilling the indices.
What are the Illustrious 18 and the Fab 4?
The Illustrious 18 are the eighteen most valuable deviations from basic strategy, ranked by how much they add to your edge — starting with taking insurance at a true count of +3. The Fab 4 are the four most valuable late-surrender deviations. Together they capture most of the playing-decision value counting makes available. The full reference lives on our Illustrious 18 & Fab 4 chart.
What is a deviation, or index play?
A deviation is a hand you play differently from basic strategy once the count is high or low enough. Each one has an index number. You normally hit 16 against a dealer 10, for instance, but at a true count of 0 or higher you stand instead. The index is the true count at which the better play flips.
Which deviation is the most valuable?
Insurance. Taking insurance at a true count of +3 or higher is the single most valuable index play, which is why it sits at the top of the Illustrious 18. After that, learn the rest of the top six, then work your way down.
Are these indices the same for every counting system?
No. The Illustrious 18 and Fab 4 index numbers are calculated for Hi-Lo specifically, which is what the large majority of counters use. Other systems have their own index values, so this trainer drills the Hi-Lo numbers.
Do I need basic strategy first?
Yes. Deviations are departures from basic strategy, so you have to know the baseline cold before the exceptions mean anything. Master it in the Basic Strategy Trainer first, then layer the deviations on top.
How do I read an index like +4?
For a playing deviation, make the count-based play — stand, double, or split — when the true count is at or above the index, otherwise follow basic strategy. For a Fab 4 surrender, surrender when the true count is at or above the index. So 15 vs 10 with an index of +4 means stand at a true count of +4 or higher, otherwise hit.