Blackjack deviations, explained
Basic strategy is the best fixed way to play every hand — but it assumes a freshly shuffled shoe. Card counters know more than that: when the true count rises or falls, the correct play for a handful of hands actually changes. Those count-driven departures from basic strategy are called deviations(or index plays), and they are where counting turns from "bet more when favorable" into playing each hand better than the chart.
How to read an index number
Every deviation is written as a hand, a dealer upcard, and a true-count threshold — the index. Take the most famous one: 16 vs 10, stand at true count 0 or higher. Basic strategy says hit 16 against a ten; the index says that once the remaining shoe is even slightly rich in high cards, busting becomes the bigger risk and standing wins more. Below the index you play basic strategy; at or above it, you make the index play. Insurance works the same way — a losing side bet by default that turns profitable at true count +3, which is why it ranks as the single most valuable deviation.
How many deviations are worth learning?
Far fewer than exist. Hundreds of indices have been published, but the value is extremely top-heavy: the ranked Illustrious 18 plus the Fab 4 surrenders capture most of what full deviation play is worth. Beyond those twenty-two, each additional index adds less and less — which is why nearly every counting curriculum stops there. For the complete picture drawn into a strategy grid, the blackjack deviation chart shows every index in its cell, including the extra hand indices beyond the core lists.
The rules change the numbers
Indices are computed for a specific game. Whether the dealer hits or stands on soft 17 moves several of them, and deck count matters too — an index memorized for a 6-deck H17 shoe isn't automatically right for a double-deck S17 game. The deviation chart lists both H17 and S17 values side by side, and the interactive strategy chart regenerates every cell for the exact rules you set — move its true-count slider and watch which plays flip.
Common questions
Should I learn deviations before basic strategy?
No. Deviations only make sense as departures from a strategy you already play perfectly — an index tells you when to override the chart, which is useless if the chart isn't automatic yet. Master basic strategy first, then add counting, then indices.
Do deviations work if I'm not counting?
No — every index is conditioned on the true count. Without a count you have no signal to deviate on, and basic strategy remains the best you can do.
How much are deviations worth compared to bet spreading?
Bet spreading is the bigger lever — most of a counter's edge comes from betting more in rich counts. Playing deviations adds a meaningful extra slice on top, and the EV heatmap puts dollar values on individual plays so you can see exactly what each spot is worth.
Where do these index numbers come from?
They're the standard published Hi-Lo indices — the same values taught by the major counting courses — and every page here renders them from the same engine that grades decisions in the trainer, so the reference and the practice table can never disagree.
Drill them until they're automatic
The free blackjack trainer keeps a live Hi-Lo count while you play and grades every decision — including deviations — against the exact indices for your table rules, with a practice mode that deals you straight into index spots at the counts where they matter.