Where the ~0.5% house edge on standard rules actually comes from
Blackjack's house edge exists for one structural reason that no strategy can remove: when both the player and the dealer bust in the same hand, the player loses first and the dealer's hand is never played out — the house effectively wins ties that a truly symmetric game wouldn't. Basic strategy (the mathematically-derived optimal play for every two-card hand against every dealer up-card) claws back most of that structural disadvantage by making the statistically-correct decision — hit, stand, double or split — for every hand, reducing what would otherwise be a multi-percent edge for an untrained player down to roughly 0.5% on a standard 3:2, multi-deck, dealer-stands-on-soft-17 game.
That 0.5% figure assumes perfect basic strategy play. Deviating from it — for example standing on a stiff 16 against a dealer's 7, or not splitting a pair of eights against a dealer's 10 — reintroduces edge back to the house, often adding multiple percentage points depending on how far the deviation is from optimal. The house edge quoted for any blackjack variant is always conditional on the player using correct basic strategy for that exact rule set; house edge and 'edge if you play randomly' are two very different numbers.
The real cost of a 6:5 blackjack payout, derived
A natural blackjack (an ace plus a ten-value card as your first two cards) occurs on approximately 4.8% of hands dealt from a standard multi-deck shoe. Under the traditional 3:2 payout, a $10 bet on a natural pays $15 profit. Under a 6:5 payout — the same hand, same cards, same probability of occurring — that same $10 bet pays only $12 profit: a $3 reduction in payout on every natural blackjack you're dealt, purely from the posted payout ratio, with nothing about your play changing.
Working the maths through: the payout reduction per natural is 0.3 units of your bet (1.5x down to 1.2x), and a natural occurs on roughly 4.8% of hands (very slightly less often when you exclude the rare case where the dealer also has a natural, since that specific hand pushes regardless of the payout ratio). Multiplying the frequency by the per-hand cost — approximately 4.8% × 0.3 — adds roughly 1.4 percentage points of house edge on top of whatever the base rule set already carries. A game that would be 0.5% house edge at 3:2 becomes roughly 1.9% at 6:5 with every other rule held identical. That 1.4-point swing, on the same cards and the same strategy, is entirely attributable to one printed number on the table felt — which is exactly why it is the first thing to check before sitting down.
Single-deck vs multi-deck, and why deck count alone isn't the whole story
All else equal, fewer decks in the shoe slightly favour the player under optimal basic strategy — the effect is usually a few hundredths of a percentage point, not a dramatic swing, because it comes from subtle changes in the probability of specific card combinations (like the frequency of ten-value cards remaining) rather than a structural change to the game. A single-deck game with identical rules (3:2 payout, dealer stands soft 17, double after split allowed) to a six-deck shoe will show a marginally lower house edge — but the difference is small enough that it is almost always dwarfed by other rule variations at the same table.
This is precisely why deck count is a weaker signal than the payout ratio and the specific rule card. A casino advertising 'single-deck blackjack' as a player-friendly headline, while quietly running a 6:5 payout, is offering a materially worse game than a standard six-deck shoe at 3:2 — the payout swing (roughly +1.4 points of house edge) is an order of magnitude larger than the deck-count benefit (a few hundredths of a point) it's implicitly trading against. Read the full rule card — payout ratio, dealer soft-17 rule, doubling and splitting restrictions, surrender availability — before assuming deck count alone tells you anything about the edge.
Frequently asked questions
What is the house edge on standard blackjack?
Roughly 0.5% under optimal basic strategy, on a typical multi-deck game with a 3:2 blackjack payout, dealer standing on soft 17, and double-after-split allowed. The exact figure shifts with each specific rule variation — payout ratio, soft-17 rule, doubling and splitting restrictions, and surrender availability all move it.
Why is 6:5 blackjack worse than 3:2?
A natural blackjack occurs on roughly 4.8% of hands. At 3:2, a $10 bet on a natural profits $15; at 6:5, the identical hand profits only $12 — a 0.3-unit cut per natural. Multiplying that cut by the natural-blackjack frequency (≈4.8% × 0.3) adds approximately 1.4 percentage points of house edge versus an otherwise identical 3:2 game.
Does playing single-deck blackjack lower the house edge?
Slightly, under identical rules — typically a few hundredths of a percentage point. But single-deck games are frequently paired with a 6:5 payout instead of 3:2, which adds roughly 1.4 percentage points of edge and completely erases (and reverses) the small deck-count benefit. Check the payout ratio before the deck count.