Rule Variations
The blackjack player will encounter many rule variations which affect the house advantage and therefore affect his chances of winning. Some rules are determined by law or regulation, others by the casino itself. Not all rules are posted, so the player may have to ask either beforehand or when the situation occurs. Over 100 variations exist.
The casino has a “house advantage” at blackjack just as it does at any other casino game. If a particular casino game has a house advantage of 5%, it means that – over the long run – the casino will win about 5% of any initial bet. As long as the blackjack player uses the best possible strategy (a strategy which is known as “Basic Strategy”), the house advantage in blackjack is less than 1%. This is very favorable to the player compared to other casino games. Of course, many blackjack players do not know Basic Strategy or do not follow it, so the true house advantage in those cases is much higher.
Dealer hits soft 17?
Each casino has a rule about whether or not the dealer hits soft 17, a rule which is printed on the table itself. In the “S17″ game, the dealer stands on all 17s. In the “H17″ game, the dealer hits on soft 17s. Of course, she always stands on hard 17s. In either case, the dealer has no choice; she either must or must not hit. The “Hit soft 17″ game is substantially less favorable to the player with about a 0.2% higher house advantage.
Number of decks
The number of decks used has a major effect on the player’s chance of winning, because it affects the house advantage. (See comparative statistics below.) All things being equal, fewer decks are more favorable for the player. (This is true for basic strategy players, even without card counting.) But all things are not equal; multi-deck games almost always have otherwise better rules than single-deck games. For illustrative purposes, the statistics below all use the same rules — double after split, dealer hits soft 17.
House Advantage by Number of Decks
Single deck 0.04%
Double deck 0.49%
Four decks 0.59%
Six decks 0.66%
Eight decks 0.69%
Surrender
Some casinos offer a favorable option called “surrender,” which allows the player to give up half his bet and not play out the hand. This option is sometimes referred to as “late” surrender because it occurs after the dealer has checked her hole card for a blackjack. (When casinos first opened in Atlantic City, the surrender option was available before the dealer checked for blackjack – a rule highly advantageous to the player – but this “early surrender” option soon disappeared.) Early Surrender variations still exist in several countries.
Resplit to nn
If the player splits a pair other than aces and a third card of that value appears, the player can usually resplit by putting up another bet equal to the original bet. Then there will be three bets on the table and three separate hands. Some casinos allow unlimited resplitting of cards other than aces, while others may limit it to a certain number of hands, such as four hands (for example, “resplit to 4″).
Resplit aces
When the player’s first two cards are two aces, the player may split them once. If a third ace appears, however, it cannot be resplit in most casinos. If resplitting aces is allowed, this is favorable to the player.
Double after split
After splitting a pair, some casinos allow the player to “double down” on each of the new two-card hands. This is called “double after split” (DAS) and provides an advantage to the player of about 0.12%.
Double on 10 or 11 only
Often called “Reno” rules, this rule restricts the player to doubling down only on an initial player total of 10 or 11 (sometimes 9, 10, or11). It prevents doubling on soft hands such as soft 17 (ace-6), and is unfavorable for the player. It increases the house advantage by about 0.20%.
European no-hole-card rule
In some places, the dealer does not receive a hole card, but if the dealer is found to have blackjack, the player loses only his original bet but not any additional ets (doubles or splits). This has the same advantage as the usual game, and as such does not change basic strategy.
Altered payout for blackjack
In some places, a blackjack pays only 6:5 or even 1:1 instead of the usual 3:2. This is the most unfavorable variation, increasing the house edge significantly more than any other player restriction.
Dealer wins ties
This is catastrophic to the player, though rarely used in standard Blackjack. It is sometimes seen in “blackjack-like” games.
Five card charlie/Five card trick
With this rule, the player always wins when five cards have been drawn without busting, unless there is a blackjack on the table.
Insurance
If the dealer’s upcard is an ace, the player is offered the option of taking Insurance before the dealer checks her ‘hole card’.
Insurance is a side bet of up to half the original bet placed on a special portion of the table usually marked “Insurance Pays 2 to 1″. The idea is that if the dealer has a blackjack, i.e., a ten-value card as her hole card, then the player is usually going to suffer the loss of his original bet. By making an extra bet of half his original bet on “insurance,” which pays 2-to-1 if the dealer has a blackjack, the “insurance proceeds” will supposedly make up for any loss on the original bet. Of course the insurance bet is forfeited if the dealer does not have blackjack, although the player can still win or lose on the original bet.
Insurance is a poor bet for the player unless he is counting cards, because the casino has a theoretical house advantage of 7.69% (“infinite deck”). The theoretical house advantage is easy to calculate, since the player is essentially betting that the dealer’s hole card is a ten-value card. To calculate it, we can use the example of a player with an original bet of £20, the dealer has an ace, and the player takes insurance for £10. In an infinite deck, 4/13 of the cards are “tens” (10, J, Q, or K). In theory, the insurance bet will lose 9/13 of the time for minus £90 and will win 4/13 of the time for plus £80, giving a net loss of £10 for 13 hands. The average loss is £0.77 per hand (10/13), or 7.69%. Therefore, taking insurance is a poor bet for the player (unless he is counting cards).
The odds on the Insurance bet are not improved if the player has a blackjack — it’s still a poor bet. Insurance is simply a side-bet that the dealer has a ten-value hole card, regardless of the player’s original cards. We can use the same example, where the player has a blackjack on his original bet of £20, the dealer has an ace, and the player takes insurance for £10. The two bets are completely separate. The player can expect on average to win £20.77 for his blackjack, since the original bet wins 9/13 of the time for a total of £270 (9 x £30) and ties 4/13 of the time for a gain of zero, for an average gain of £20.77 per hand (£270/13). Meanwhile, the insurance side bet of £10 is calculated separately and loses £0.77 on average. Therefore, on average, the player would win £20.77 for his blackjack on his original bet, and would lose £0.77 on the £10 insurance bet, if he takes insurance. The insurance bet is still not worthwhile (unless, again, the player is counting cards).
A variation on this is that some casinos or dealers may offer the player what they call “even money” by offering to pay out the blackjack at 1:1 when the upcard is an ace. This is exactly the same as taking insurance, although the player does not have to put up the insurance bet. Again, the player’s expectation for the “even money” option is £20.00, instead of an average of £20.77, so it’s not a favorable bet (unless the player is counting cards).
In casinos where a hole card is dealt, a dealer who is showing a card with a value of Ace or 10 may slide the corner of her hole card over a small mirror or electronic sensor on the tabletop in order to check whether she has a blackjack. This practice minimizes the risk of inadvertently revealing the hole card, which may give the sharp-eyed player a considerable advantage.