If you've ever played blackjack, you already know that if you get two identical cards in a hand, you can split them into two separate hands. This action is referred to as a "split". These two hands are then treated as two separate players. Each of them may be split again (in case of getting another identical card) or doubled.

The basic strategy for blackjack clearly defines the situations when the player should split cards in blackjack and when to play without splitting them. This knowledge is absolutely crucial for most professional players because it reduces the house edge and in addition, gives the player a substantial chance of winning.

Generally speaking, according to the optimal strategy, there are three options for a hand consisting of two identical cards:

• Always split pairs
• Never split pairs
• Play by dealer's card

Always Split Pairs In Blackjack

Remembering when it's always good to split in blackjack is easy. This rule only applies to two pairs – aces and eights. There is a very simple reason for splitting aces. The maximum value of two aces is 12 (11 + 1). The only card to make a blackjack from 12 is 9. A much more likely scenario occurs when the player gets another card with a value of 10. This case may result either in bust (exceeded 21) or a 12 (1 + 1 + 10).

The logic behind splitting eights is very similar. The value of a pair of eights is only 16, which is a very unfortunate sum in blackjack. It is too low for winning and too high for a hit because more than two-thirds of the cards in the deck will get you over 21.

Some casinos allow a so-called resplit – splitting of a pair that has already been split. The same rule applies here, too. If possible, always resplit both eights and aces.

Never Split Pairs in Blackjack

Although it may seem illogical, it is true that a player should never split a pair of cards with a value of 10. Why? The total value is 20, which is very good and the only thing that trumps such a pair is getting an ace. The probability of this happening is, however, very small and the player is more likely to get two lower-value hands.

The next pair that should never be split is a pair of fives. By splitting them you only get a worse starting position with two weak hands. In addition, a sum of 10 is advantageous, especially if the dealer's face card has the same or lower value.

Play by the dealer's card

The remaining pairs are split depending on the dealer's face card to maximize the mathematical probability of winning. The following rules apply:

• 2, 3 and 7 – always split if the dealer's face card is 7 or lower
• 4 - split only if the dealer's face card is 5 or 6
• 6 - split only if the dealer's face card is 6 or lower
• 9 - always split except when dealer's face card is 7, 10 or ace

To remember this strategy better, follow the table below.

Legend:

Splitting pairs for card counters

As usual with blackjack, players using card counting techniques may in some cases deviate from the optimal strategy. Most often we see this in case of insurance that is otherwise considered disadvantageous – a sucker bet. However, this is also the case with the splitting rules. In some cases, card counters shouldn't split a pair of aces or should split a pair of tens.

First, we will show how card counting can affect the player's decision. If the card count is high and positive (e.g. +5, +6 or more), it is obviously advantageous to split the aces because the player knows that the deck contains more cards worth 10 which means a greater chance of blackjack.

The player will not split aces if the value is negative. In this case, the deck contains fewer cards with a value lower than 10. At the same time, the dealer should have a high card, i.e. a card with a value of 8, 9 or 10. We'll show an example.

Let's say the player has two aces and his count is -5. The dealer has a card with a value of 10. The player splits the pair according to the optimal strategy, and the next cards he gets are 3 and 5. After splitting, it is no longer possible to play, so he has to face the dealer's card with a value of 10 and hands worth only 14 and 16, respectively. That is not a very pleasant situation. In such a case, it is better not to split the aces and rather draw another card, because regardless of what the player gets, he can't bust.

The same logic can also be applied to the decision whether to split cards worth 10. Generally, we should never split these cards, but there is an exception that applies if the count is negative and the dealer has a low card (e.g. 4, 5 or 6). The player thus has a higher chance of getting at least 20 on one of the hands, which is very hard to beat with a low card.