Blackjack Odds, Probability, and House Edge
Blackjack is one of the best-known casino games worldwide. Its blend of chance and player decisions helps explain its enduring appeal. Basic strategy can substantially reduce the house edge: depending on the rules, some cited figures drop from 8% to as low as 0.5%. A lower edge improves the mathematical return over time, but does not guarantee a win in any session.
House Edge vs. Payout Percentage
The house edge represents the casino's expected share of wagers over time. It is calculated by applying the edge percentage to the total amount wagered, assuming the player uses optimal strategy. This measure applies to games such as blackjack, although the rules affect the figure.
House edge and payout percentage are inverse figures that add up to 100%. The payout percentage, also known as the return percentage, estimates the share of all wagers that players receive back on average.
Payout calculations also assume optimal play. They show the average return over many blackjack hands, not what any one player is guaranteed to receive.
To see how payout percentage relates to house edge, consider an Atlantic City Blackjack game with a stated payout percentage of 97%. Subtracting 97 from 100 gives a 3% house edge.
A 3% edge and a 97% payout describe the same relationship from opposite sides. On average, the example means the casino keeps $3 for every $100 wagered over time.
These figures represent averages over tens of thousands of hands, and an individual outcome may differ considerably. A player using little or no strategy might see a 56% payout, while a player following sound strategy who also gets lucky might reach 134%—a $34 profit for every $100 wagered. Neither figure predicts the outcome of a future session.
House Advantage in Banker Games
Games such as casino games including roulette, baccarat, craps and blackjack are often called banker’s games. Players compete 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 to keep some wagers, regardless of how a player approaches the game.
In blackjack, a losing player's bet goes to the dealer, whatever the dealer's hand total. A player wins a payout by beating the dealer, while the dealer collects the wager if the player busts.
True Odds vs. Casino Odds
The casino also determines the payouts for each result. This creates a difference between the true odds of an event and the payout odds offered by the casino. Players decide whether to accept the terms on offer.
Take a standard die numbered 1 through 6 to compare true odds with casino odds. The true odds of rolling a 2 are 1 in 6, giving the player a 16.666% chance of landing on 2.
A casino might pay less than 6 to 1 on a bet that the die will land on 2, perhaps offering 5 to 1 or even 4 to 1. It still collects losing bets in full, while a winning player receives less than the true odds would suggest.
Low House Edge
Casinos have an advantage in most games, but blackjack often has a comparatively low house edge. For context, Keno is cited at 25% to 29%, while American roulette has a 5.26% edge on single-number bets. These comparisons help explain why blackjack is known for a relatively small house advantage.
Blackjack combines decisions with chance. According to the figures cited here, players using basic strategy may face an average house edge of 0.17% in a single-deck game, increasing to 0.66% in an 8-deck game.
Fewer decks generally mean a lower house edge. To preserve the casino's advantage in single-deck games, the payout for a natural blackjack may be reduced.
Review a blackjack variant's specific rules before comparing its house edge with another game. Some rules favour the casino more and can increase the edge to 1% or higher.
The Odds of Busting
A bust happens when a hand total goes over 21. Before hitting—that is, drawing another card—consider how the risk of busting changes with your current hand total. These probabilities can help inform a decision, but they cannot guarantee a winning 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% |
How the Number of Decks Affects House Edge
Blackjack is often seen as relatively player-friendly because it combines chance with decisions that can affect the house edge. Basic strategy can bring the edge below 1% in many variations, though the exact figure depends on the rules.
Number of Decks in Play
The number of decks affects the house edge in many blackjack variations. Some variants require a fixed deck count because changing it would conflict with their rules.
Other blackjack games can be offered with different deck counts. Depending on the number of decks and the other rules, this can increase or decrease the house edge.
Generally, games with fewer decks have a lower house edge. With optimal basic strategy, that also means a higher expected payout percentage for the player.
Why the Number of Decks Matters
The number of decks matters in part because it changes the probability of being dealt a natural blackjack.
With fewer decks in play, a player who receives a 10-value first card has a better chance of drawing an Ace as the second card and completing a natural blackjack.
Fewer decks also make it less likely that the dealer will have a natural blackjack at the same time. When both have one, the hand is a tie and the player's wager is returned as a push.
The Actual Percentages
To compare the effect of deck count on the house edge, keep one set of rules constant and change 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 if the dealer shows blackjack
- A cut card is used
The table below matches the number of decks to the house edge under the blackjack rules listed above:
| Number 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% |
How Blackjack Rule Changes Affect the House Edge
More than 100 blackjack variations have been recorded over the years. Some use a set group of rules, while others let casinos select rules when they offer a particular version.
Changes to blackjack rules influence the house edge and the percentage of wagers players may receive back over time.
Deck Count
Fewer decks generally lower the house edge for two key reasons:
- With fewer decks, a player whose first card is worth 10 has a better chance of drawing an ace next and making a natural blackjack.
- With fewer decks, it is less likely that both the player and dealer will have blackjack, pushing the player’s wager.
Resplitting
After splitting a pair, players may sometimes split again if a new hand contains two cards of equal value. Tables may limit the number of hands—for example, to 4—or permit unlimited splits. In general, allowing more resplits reduces the house edge and is more favorable to the player.
Dealer Hits Soft 17
Each blackjack version sets the dealer’s required actions, including whether to hit or stand on soft 17. The dealer follows that rule rather than making a choice during play. Generally, standing on soft 17 favors the player, reducing the house edge by around 0.2%.
Late Surrender
Late surrender allows a player to give up after the first two cards if they think the hand is unlikely to beat or tie the dealer. Half the original wager is forfeited and the rest is returned. This player-friendly option can lower the house edge by up to 0.1%.
Doubling After a Split
Many games allow players to double down after splitting. Compared with an otherwise identical game that disallows it, this rule reduces the house edge by about 0.12%.
Resplitting Aces / Hitting Split Aces
Many games prohibit resplitting aces and limit each split-ace hand to one additional card; players cannot hit, double or split again. Where permitted, these actions improve the player’s terms: hitting split aces lowers the house edge by more than 0.1%, while resplitting aces reduces it by around 0.03%.
Natural Blackjack Payout Changes
A natural blackjack usually pays 3:2. Some games, especially 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 increases it by about 2.3%.
