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. Everything else builds on it.
The seven guides
Basic Strategy
The foundation — the mathematically optimal play for every hand, derived from computer simulation. Reduces the house edge to roughly 0.5%.
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.
How to use this guide
Read 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 all seven 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.
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.