Blackjack Odds, Probability and House Edge
Blackjack has become one of the best-known casino games around the world. Its mix of chance and decisions helps explain its lasting appeal. Using basic strategy can reduce the house edge substantially: depending on the rules, a figure cited for some games falls from 8% to as low as 0.5%. A smaller edge improves the mathematical return over time, but does not ensure a win in any session.
House Edge vs. Payout Percentage
The house edge describes the casino’s expected share of wagers over time. It is calculated by applying the edge percentage to the total amount wagered while assuming the player follows optimal strategy. This measure is relevant across games such as blackjack, though each game’s rules affect its value.
House edge and payout percentage are complementary figures: together they equal 100%. The payout percentage, also called return percentage, estimates the portion of all money wagered that players receive back on average.
A payout calculation also assumes optimal play. It represents the average return across many blackjack hands, rather than a promise about what an individual player will receive.
To see how payout percentage relates to house edge, consider an Atlantic City Blackjack game with a stated payout percentage of 97%. The calculation is 100 minus 97 = 3%, giving the house edge.
So a 3% edge and a 97% payout express the same relationship from opposite sides. On average, the example implies the casino keeps $3 from each $100 wagered over time.
These figures describe averages across tens of thousands of hands, and an individual result can differ greatly. A player using poor or no strategy might see a 56% payout, while another who follows sound strategy and also benefits from luck might reach 134%—a $34 profit for every $100 wagered. Neither result predicts what will happen in a later session.
House Advantage in Banker Games
Games such as casino games including roulette, baccarat, craps and blackjack are often called banker’s games. The player competes against the house, represented by a dealer or croupier, and the rules give the house an unequal advantage.
The structure of these games gives the house an overall chance of retaining some wagers, regardless of a player’s approach.
When a blackjack player loses, their bet goes to the dealer, whatever value the dealer’s hand holds. A player collects a payout by beating the dealer, while the dealer can take the bet if the player busts out.
True Odds vs. Casino Odds
The casino also sets the payouts attached to each outcome. That creates a distinction between the true odds of an event and the odds the casino offers to pay. Players must choose whether to accept the available terms.
Consider one regulation playing die, numbered from 1 to 6, to distinguish true odds from casino odds. The true odds of throwing a 2 are 1 in 6, which gives the player a 16.666% chance of the die landing on 2.
A casino may pay less than 6 to 1 on a wager that the die will show 2, perhaps offering 5 to 1 or even 4 to 1. It still collects losing wagers in full, while a winning player receives less than the true odds would indicate.
Low House Edge
Although casinos hold an advantage in most games, blackjack often has a comparatively low house edge. For perspective, Keno is cited at 25% to 29%, while American roulette has a 5.26% edge on single-number bets. These comparisons help explain blackjack’s reputation as a game with a relatively small house advantage.
Blackjack involves decisions as well as chance. Players who use basic strategy may face an average house edge of 0.17% in a single-deck game, rising to 0.66% in an 8-deck game, according to the figures cited here.
Fewer decks generally correspond to a lower house edge. To retain an advantage for the casino in single-deck games, the payout for a natural blackjack may be reduced.
Check the specific rules of a blackjack variant before comparing its edge with another game. Some rule sets favour the casino more strongly and can raise the house edge to 1% or higher.
The odds of Busting
A bust occurs when a hand total exceeds 21. Before deciding whether to hit—that is, draw another card—it helps to consider how the chance of busting changes with the value of your current hand. Those probabilities can inform a decision, though they cannot guarantee that it will win the hand.
| Total Hand Value | Odds of Busting when Hitting |
|---|---|
| 21 | 100% |
| 20 | 92% |
| 19 | 85% |
| 18 | 77% |
| 17 | 69% |
| 16 | 62% |
| 15 | 58% |
| 14 | 56% |
| 13 | 39% |
| 12 | 31% |
| 11 or less | 0% |
The Effects of Number of Decks on House Edge
Blackjack is often described as relatively player-friendly because it combines chance with decisions that can affect the house edge. Applying basic strategy can bring the edge below 1% in many variations, although the exact result depends on the rules in play.
Number of Decks in Play
Deck count affects the house edge in many blackjack variations. Some versions require a set number of decks because changing that count would conflict with their rules.
Other blackjack versions can be offered with different deck counts. The change can raise or lower the house edge, depending on how many decks are used and on the other rules governing play.
In general, games with fewer decks tend to have a lower house edge. With optimal basic strategy, that also corresponds to a higher expected payout percentage for the player.
Why Number of Decks Matters
Deck count matters partly because it changes the probability of being dealt a natural blackjack.
With fewer decks in play, a player who receives a 10-valued first card has a greater chance of drawing an ace as the second card, completing a natural blackjack.
Fewer decks also reduce the chance that the dealer has a natural blackjack at the same time as the player. When both have one, the hand is a tie and the player’s wager is returned as a push.
The Real Percentages
To compare how deck count affects the house edge, consider one fixed set of rules and vary only the number of decks in play.
Rules used:
- Doubling is allowed on any two cards
- The dealer hits on soft 17
- Doubling after a split is allowed
- Resplitting is allowed up to 4 hands
- Surrender is not allowed
- Players cannot hit split aces
- Only the player’s original bet is lost when the dealer shows blackjack
- A cut card is used
The table below pairs the number of decks with the corresponding house edge under the blackjack rules listed above:
| No. of Decks in Play | House Edge |
|---|---|
| Single Deck | 0.17% |
| Double Deck | 0.46% |
| Four Decks | 0.60% |
| Six Decks | 0.64% |
| Eight Decks | 0.66% |
Effects of Blackjack Rules Variations on House Edge
More than 100 blackjack variations have been documented over the years. Some keep a fixed rule set, while others allow the casino to choose which rules to include when offering a particular version.
Adjustments to blackjack rules affect both the casino’s house edge and the payout percentage a player may receive over time.
Number of decks
Using fewer decks usually reduces the house edge for two main reasons:
- With fewer decks, a player dealt a 10-valued first card has a higher chance of drawing an ace next and making a natural blackjack.
- Fewer decks make it less likely that both the player and dealer have blackjack, which would push the player’s wager.
Resplitting
After splitting a pair, a player may sometimes split again if the new hand contains cards of equal value. Tables can cap the number of split hands—for example, at 4—or allow unlimited splits. Generally, more permitted resplitting lowers the house edge and gives the player a more favourable rule.
Dealer hits soft 17
Each blackjack variant sets rules for how the dealer must act, including whether to hit or stand on soft 17. The dealer follows that fixed rule rather than choosing during play. Generally, a dealer standing on soft 17 is more favourable to the player because it reduces the house edge by around 0.2%.
Late surrender
Late surrender lets a player give up a hand after the first two cards when they judge it unlikely to beat the dealer or tie. The player forfeits half the original bet and receives the other half back. This option favours the player and can reduce the house edge by up to 0.1%.
Double after split allowed
Many games permit doubling down after a split. Compared with an otherwise identical game that prohibits it, this rule lowers the house edge by about 0.12%.
Resplitting aces/ Hit resplit aces
Many games prohibit resplitting aces and restrict each split ace hand to one additional card; players cannot hit, double or split again. Where the rules allow these actions, the terms are more favourable to the player: hitting after splitting aces lowers the house edge by more than 0.1%, while allowing aces to be resplit reduces it by around 0.03%.
Changes to natural blackjack payouts
A natural blackjack usually pays 3:2. Some games, particularly single-deck versions, instead pay 6:5 or 1:1. A 6:5 payout adds about 1.4% to the house edge, while a 1:1 payout raises it by about 2.3%.
