Blackjack basic strategy, and the house edge it leaves behind
A player following basic strategy still faces a house edge, usually between 0.5% and 1%, because the rules of blackjack are built to favour the dealer regardless of skill.
Blackjack basic strategy is a fixed set of decisions for every possible hand a player can be dealt, based on two pieces of information: the player's own total and the dealer's visible card. For each combination, there is a mathematically determined best action: hit, stand, double down, split or surrender.
The strategy was first worked out properly in a 1956 paper by Roger Baldwin, Wilbert Cantey, Herbert Maisel and James McDermott, published in the Journal of the American Statistical Association under the title "The Optimum Strategy in Blackjack". It was the first mathematically sound optimal strategy for the game, and it became the foundation for later work. Ed Thorp later used Baldwin's hand calculations to verify the approach and set it out for a wider audience in his 1963 book Beat the Dealer.
Why the dealer keeps an edge anyway
Basic strategy does not change the underlying rules of blackjack, and those rules still favour the house. The largest single source of that edge is the fact that a player who busts loses immediately, even if the dealer goes on to bust as well. Basic strategy reduces unnecessary losses within that structure; it cannot remove the structural advantage itself.
According to Wikipedia, a player using basic strategy loses, on average, less than 1% of the money they put into action over the long run, which puts blackjack among the lowest house edges of any casino game. Figures for the house edge that casinos and gaming regulators quote are generally calculated on the assumption that players are using basic strategy. Most blackjack games carry a house edge of between 0.5% and 1%.
Straying from basic strategy does not help the player; deviating from it only increases the house's edge further. One example given is that taking insurance, or so-called "even money" on a player blackjack, is never the correct play under basic strategy, regardless of the specific game's rules.
The rules themselves move the number
Because the edge is built into the rules rather than the player's choices, specific rule variants shift it even when basic strategy is followed correctly. Paying 6:5 on a blackjack instead of the standard 3:2 increases the house edge by about 1.4%. A dealer required to stand on soft 17 (S17) is better for the player than one required to hit it (H17), cutting the edge by around 0.2%. Restricting doubling down to hard totals of 9, 10 or 11 — the so-called Reno rule — adds roughly 0.1% to the house edge, or about 0.2% under its stricter European version. Playing without a hole card, where the dealer does not look at their second card until players have acted, adds around 0.11%.
A more refined version, composition-dependent strategy, factors in not just a hand's total but which specific cards make it up. Wikipedia notes this can trim the house edge further, by 0.04% in a single-deck game and by just 0.003% in a six-deck game — a difference so small in multi-deck games that it is rarely worth the added complexity.
What the percentage does not mean
None of these figures describe what happens in any individual session. A house edge of under 1% is a long-run average across very large numbers of hands; it does not prevent a player from losing a given session, nor does it guarantee recovering losses over time. Basic strategy lowers the rate at which a player is expected to lose money against the game's built-in rules — it does not convert blackjack into a game with a positive expectation for the player.