When it comes to splitting pairs, most players don’t have a clue. They either always split or never split or worse rely on hunches and end up splitting recklessly. This is unfortunate because pair splitting was introduced into the game of blackjack as a way for players to reduce the casino’s edge. But nowadays, this rule is a big money maker for the casinos. But it doesn’t have to be this way – not if you understand the simple rules for when to split and the logic behind it.

There are three reasons why it would make sense to split a pair instead of standing or hitting. You should opt for pair splitting when:
You will gain more money on average (bold strategy)
You will lose less money on average (defensive strategy)
You turn a losing hand into a winning hand (offensive strategy)
Let’s take a look at the bold strategy for pair splitting. These are hands in which you are the favorite to win but by splitting you will win more. An example of this is when you are dealt a pair of 9’s and the dealer shows a 6 upcard. You’re the favorite to win if you stand with the 18. In fact if you bet one dollar a hand you stand to gain 28 cents by standing on the 18.
Compare this with pair splitting. Here you must put up another dollar and play out two hands, each one starting with a count of 9. On the surface it seems that starting a hand with a count of 18 is better than starting a hand with a count of 8. In fact that’s correct. You will win more hands when you have an 18 against a dealer 6 face card compared to starting with a count of 8. So how can pair splitting be the better play? Because what matters when you play blackjack is not how many hands you win but how much money you stand to gain.
If you look at the profit potential of your two choices – standing on 9,9 (18) or splitting the 9’s, here is what you’ll find.
If you stand with a pair of 9’s you will win 64% of the time and lose 36%. If you bet $1 per hand your average win per hundred dollars bet is $28 or a profit of 28 cents per hand.
If you split you will win less -60%- and lose 40% of the hands on average. However, because you double your bet each time you split your average gain is $20 times 2 or $40 which equates to a profit of 40 cents per hand.

It all boils down to which is better:
Winning a dollar 28% of the time or winning two dollars 20% of the time.
Even though you win less hands when you split you win more money because you bet more. Therefore, splitting a pair of 9’s is the preferred strategy when the dealer shows a 6.
The defensive strategy for pair splitting is used to cut your losses in a losing situation. This might seem confusing but here’s an example of how this works.
Suppose you are dealt a pair of 7’s and the dealer shows a 2. You’ll agree that a 14 is a lousy hand. If you stand you will win on average only 36% of the time on average and lose 64%. Your expected loss per hand is 28 cents. In other words standing on a pair of 7’s (14) is a loser against a dealer 2 upcard.

Suppose instead you split the 7’s. You start each split hand with a count of 7, which is slightly better than a 14 against a 2. But you are still the underdog, even with a 7. You will win 45% of the hands on average and lose 55%. Your net loss per hand is 20 cents. Yes that’s still a loser but is it better to lose 20 cents or 28 cents? That’s right you should go with the play that cuts your losses, which in this case is to split the 7’s.
Offensive pair splitting is the best kind of splitting because it turns a losing hand into one that will win you money. An example is a pair of 7’s against a dealer 6 upcard.
If you stand with the 14 you will win on average 42% of the hands and lose 58% for an average loss per hand 16 cents. By pair splitting, you are now playing two hands with a starting count of 7 in each hand. This is much stronger than starting with a count of 14 with the dealer showing a 6. In fact you win 52% of those hands and lose 48% for a net eight-cent profit per hand. By splitting offensively you’ve turned a 16-cent deficit into an overall gain of 8 cents.

A summary of the correct pair splitting rules for multiple deck games that allow you to double down following a split (DAS) is:

Split 2’s, 3’s and 7’s against a dealer’s 2 through 7
Split 4’s against a dealer’s 5 and 6
Split 6’s against a dealer’s 2 though 6
Split 9’s against a dealer’s 2 through 6 plus 8 and 9.
Always split aces and 8’s
Never split 5’s and 10’s
If DAS is not allowed, you would split less often. The pair splitting rules in this case is:
Split 2’s, and 3’s against a dealer’s 4 through 7
Split 6’s against a dealer’s 3 through 6
Split 7’s against a dealer’s 2 through 7
Split 9’s against a dealers 2 through 6 plus 8 and 9
Always split aces and 8’s
Never split 4’s, 5’s, and 10’s

Learning when to pair split is one way you can win more (or lose less) when you play blackjack. Don’t pass up the opportunity to do so.