Blackjack Strategy Trainer 21
What this guide covers
Blackjack is one of the few casino games where correct play meaningfully changes the math. Played with basic strategy at a standard 6-deck S17 table with DAS and late surrender, the house edge drops to about 0.43% — the lowest of any common casino game without skill (or counting). Played by intuition, the same game runs 2% or worse. The gap between those two outcomes is everything covered here.
Every page in this section is derived from the same source: computer simulation of billions of hands against fixed dealer rules. Nothing here is opinion. The decisions are the mathematically optimal play for the given rule set.
Start here
If you read one page in this section, make it Basic Strategy. It's the full chart — every hand, every dealer up-card, every action — with the reasoning behind the non-obvious cells. Want just the table? Jump straight to the basic strategy chart. Everything else builds on it.
Core guides
Basic Strategy
The foundation — the mathematically optimal play for every hand, derived from computer simulation. Reduces the house edge to roughly 0.5%.
Basic Strategy Chart
The full S17 six-deck decision table — hard totals, soft totals and pairs — color-coded in one place. The chart you came for.
S17 vs H17
How the soft 17 rule changes the dealer's behavior, swings the house edge by 0.22%, and flips six cells of basic strategy.
When to Double Down
The exact hands and dealer up-cards where doubling your bet maximizes expected value — and when "double for less" is a leak.
When to Split
The pair-splitting rules: always split Aces and 8s, never split 5s or 10s, and the seven middle pairs that depend on the dealer's up-card.
When to Surrender
Late surrender done right — the four hands worth surrendering and why folding half your bet beats playing some hands out.
House Edge
How each rule — decks, soft 17, surrender, DAS, payout — adds or subtracts from the house edge, with numbers for every combination.
How to Memorize Basic Strategy
Spaced repetition, pattern grouping, and the order to learn the chart in. Most players reach perfect recall in 4–6 hours of focused practice.
Search-demand guides
These shorter guides answer the exact blackjack strategy questions players search after hitting a confusing rule, pair, or trainer decision.
Blackjack Basic Strategy Trainer
How to practice every hand category with feedback, rule-set toggles, and spaced repetition instead of rereading a chart.
Blackjack Split Rules
The casino mechanics behind pair splitting, resplits, split aces, DAS, and the rules that change the chart.
What Is Splitting?
A plain-English explanation of what splitting does, when it creates two hands, and why it changes the bet size.
What Cards to Split
A compact split-by-pair lookup for aces, 8s, 9s, 7s, 6s, 5s, 4s, and ten-value cards.
When Can You Split?
The practical rules for eligible pairs, same-rank restrictions, ten-value cards, and table limits.
Soft 17 Blackjack
What soft 17 means, why the dealer rule matters, and how it connects to S17 and H17 strategy.
S17 Basic Strategy
The clean baseline chart for games where the dealer stands on all 17s.
H17 Basic Strategy
The adjusted strategy for tables where the dealer hits soft 17, including the six cells that flip.
Pair-specific split answers
Use these pages when you want the fast answer for a single pair without scanning the full chart.
When to Split Aces
Why A,A is split against every dealer upcard, even with the one-card restriction after the split.
When to Split 8s
Why splitting 8,8 is usually the best way to escape the worst hard total in blackjack.
When to Split 10s
The basic-strategy answer is almost never: 20 is too strong to break up without count information.
When to Split 9s
The overlooked 9,9 chart: split against 2-6, 8, and 9, but stand against 7, 10, and Ace.
Should You Split 5s?
No: 5,5 is hard 10, so it belongs in the double-down chart rather than the split chart.
How to use this guide
Read the core guides in this order — each page assumes you've internalized the previous ones:
- Basic Strategy — get the full chart in your head first.
- S17 vs H17 — learn which rule your table uses and the six cells that change.
- When to Double Down — drill the doubling decisions, they're where most casual players leak EV.
- When to Split — clean up the pair-splitting cells, especially 9,9 and 4,4.
- When to Surrender — add surrender if your table offers it. Many don't.
- House Edge — understand which rules to chase and which to ignore.
- How to Memorize — the practice loop that locks it in for good.
Total reading time across the core pages is about 90 minutes. Total practice time to reach reliable recall at the table is closer to five hours — most of it in short sessions over a week or two. Use the shorter search-demand guides when a specific table rule or pair decision needs a direct answer.
Practice with the app
Reading the chart is not the same as recalling it under pressure. Blackjack Strategy Trainer 21 is a free Android app that drills the full chart with spaced repetition: the cells you get wrong come back more often, the cells you nail get spaced further apart. You can switch between S17 and H17 rule sets and toggle surrender and DAS to match the game you actually play.
Get the free Android trainer
No signup, no ads in the way of practice, no paywall on the chart. Train basic strategy until it's automatic.