Blackjack Odds, Probability and House Edge
Blackjack is one of the world's best-known casino games. Its combination of chance and decision-making helps explain its enduring appeal. Basic strategy can significantly reduce the house edge: depending on the rules, some games are cited as going from 8% to as little as 0.5%. A lower edge improves the mathematical return over time, but doesn't 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's calculated by applying the edge percentage to the total amount wagered, assuming the player follows optimal strategy. The measure applies to games such as blackjack, though the rules affect the figure.
House edge and payout percentage are complementary: together they equal 100%. The payout percentage, also known as the return percentage, estimates the share of all wagered money that players receive back on average.
Payout calculations also assume optimal play. They represent average returns over many blackjack hands, not a promise of what an individual player will get back.
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%, which is the house edge.
A 3% edge and a 97% payout describe the same relationship from opposite sides. In this example, the casino keeps an average of $3 from every $100 wagered over time.
These numbers reflect averages over tens of thousands of hands, and an individual result can vary greatly. A player using little or no strategy might see a 56% payout, while another who plays soundly and also gets lucky might reach 134%—a $34 profit for every $100 wagered. Neither outcome predicts what will happen in a future session.
House Advantage in Banker Games
Games such as casino games including roulette, baccarat, craps and blackjack are often known as banker’s games. The player competes against the house, represented by a dealer or croupier, and the rules give the house an advantage.
The structure of these games gives the house an overall chance of keeping some wagers, regardless of the player's approach.
When a blackjack player loses, the dealer takes the bet, whatever the dealer's hand total. The player wins a payout by beating the dealer, while the dealer can collect the wager if the player busts.
True Odds vs. Casino Odds
The casino also sets payouts for each outcome. This creates a difference between the true odds of an event and the odds the casino offers to pay. Players decide whether to accept the available terms.
Take a standard playing die numbered from 1 to 6 to see the difference between true odds and casino odds. The true odds of rolling a 2 are 1 in 6, giving the player a 16.666% chance of the die 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. The casino still collects losing wagers 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 relatively low house edge. For comparison, Keno is cited at 25% to 29%, while American roulette has a 5.26% edge on single-number bets. These figures help explain blackjack's reputation for having a comparatively 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 maintain a casino advantage in single-deck games, the payout for a natural blackjack may be reduced.
Check the rules of each blackjack variant before comparing its edge with another game. Some rule sets favour the casino more and can push the house edge to 1% or higher.
The Odds of Busting
A hand busts when its total goes above 21. Before choosing whether to hit—that is, take another card—it helps to consider how your bust risk changes with your current hand value. These probabilities can inform your decision, but they can't 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 considered relatively player-friendly because it combines chance with decisions that can influence 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 versions require a set number of decks because changing that number would conflict with their rules.
Other blackjack games may be offered with different numbers of decks. This can raise or lower the house edge depending on the deck count and the other rules in effect.
Generally, games with fewer decks have a lower house edge. With optimal basic strategy, this 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 gets a 10-value card first has a greater chance of drawing an ace next and making a natural blackjack.
Fewer decks also lower the chance that the dealer and player will both have a natural blackjack. If they do, the hand is a tie, and the player's wager is returned as a push.
The Real Percentages
To compare the effect of deck count on the house edge, keep the rules fixed 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 shows the house edge for different deck counts 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 follow a set collection of rules, while others let the casino select the rules for a specific version.
Changes to blackjack rules influence the casino’s house edge and the payout percentage players may receive over time.
Number of Decks
Fewer decks generally lower the house edge for two key reasons:
- With fewer decks, a player whose first card is worth 10 is more likely to receive an ace next and make a natural blackjack.
- With fewer decks, it is less likely that both the player and dealer will have blackjack, resulting in a Push that returns the player’s wager.
Resplitting
After splitting a pair, players may sometimes split again if a new hand has cards of equal value. The maximum number of hands varies: a table might limit players to 4, for example, or permit unlimited splits. In general, greater freedom to resplit lowers the house edge and favours the player.
Dealer Hits Soft 17
Every blackjack variant sets out how the dealer must play, including whether to hit or stand on soft 17. The dealer follows the table’s rule rather than making a choice during the hand. Generally, standing on soft 17 benefits the player, lowering the house edge by about 0.2%.
Late Surrender
Late surrender allows a player to give up after the first two cards if they believe the hand is unlikely to beat or tie the dealer. Half the original wager is forfeited, and the other half 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 does not allow it, this rule reduces the house edge by about 0.12%.
Resplitting Aces / Hitting Split Aces
Many games do not allow aces to be resplit and limit each split-ace hand to one extra card; players cannot hit, double or split again. Where these moves are allowed, the rules favour the player: hitting split aces lowers the house edge by more than 0.1%, while allowing aces to be resplit lowers it by about 0.03%.
Changes to Natural Blackjack Payouts
A natural blackjack typically pays 3:2. Some games, particularly single-deck versions, instead pay 6:5 or 1:1. A 6:5 payout increases the house edge by about 1.4%, while a 1:1 payout raises it by about 2.3%.
