Splitting 10s

There are two types of blackjack players that split a pair of 10s. One type is the casual player that has no idea what the right playing strategies are for blackjack. The other is the pro that knows the game inside and out. How can splitting 10s be bad for the casual player and good for the pro? Read on and I'll explain.

Most casual players split 10s when the dealer has a weak up card like a 5 or 6 (although I have seen many players during my career split 10s no matter what the dealer shows). Their logic for splitting on the dealer's 5 or 6 goes something like this: "The dealer has a weak card and I've got a good chance to make two good hands starting with a 10, so why not split and double my winnings". Oh, really.

Let's look at your expected value, the average amount you would win per hand, when you stand compared to when you split. Computer simulation tells us that when you stand on a pair of 10s against a dealer's 6 up-card, you will win 85 percent of the time. That's not too surprising because it's tough for the dealer to beat a strong hand of 20. If you split the 10s, the computer results show that you will win only 64 percent of the hand. That's a significant decrease in the number of hands won simply because if you split you will often end up with less than 20 on both hands.

Of course when you split you will be doubling your bet. Therefore to compare the expected value of splitting over standing, the question we need to answer is this, "Is it better to win $1 85 percent of the time or $2 64 percent of the time"? Let's do the quick math and find out.

Standing
In 100 tries I expect to win one dollar 85 times and lose one dollar 15 times and thus be ahead $70 ($85-$15). This is a net expectation of 70 cents per hand.

Splitting
In 100 tries I expect to win two dollars 64 percent of the time and lose two dollars 36 percent of the time and thus be ahead $56 ($128-$72). This is a net expectation of 56 cents per hand.

Yes, you will make money if you split 10s when the dealer shows a 6 up card to the tune of 56 cents per hand. However, you will make 14 cents more per hand on average if you stand (70 cents vs. 56 cents). This is why standing on a pair of 10s is the preferred play.

If you do the same analysis for 10s against a dealer 5 you'll arrive at a gain of expectation of 16 cents per hand when you stand vs. split making standing the more profitable play.

If it's more profitable to stand on 20 rather than split, why do the pros sometimes split? The answer to this has to do with the composition of the undealt cards.

The above analysis was done assuming the top-of-the-deck composition of cards. In practice the composition of the cards changes from hand to hand depending upon the cards played. The pros carefully watch the cards played so they have useful information on the composition of the undealt cards. So, if a pro sees a lot more small value cards being played compared to the 10s, picture cards, and aces, then he knows that the undealt cards must have a higher proportion of the latter cards. This will be the ideal time to split the 10s since the chances are greater of drawing two tens or aces for pat 20 or 21 hands. Also, the pro knows that if the dealer has a 5 or 6, he must draw a third card (unless he has an ace-6) and the probability is great that he will break when he draws from a ten-rich deck.

The only way you are going to know when the undealt cards become rich enough in 10s and aces to make splitting 10s a more profitable play than standing is to learn a card counting system. For example, for the popular High Low counting system, the pro would split 10s against a 6 when there is an excess of 4 more high value cards per deck than normal. Although this doesn't happen too often, when it does, the pro knows that his expectation is greater when he splits compared to standing.

The bottom line for splitting tens is this -- if you are a casual player, never split 10s no matter what the dealer shows because in the long run that bird in the hand (20) is worth a lot more than two in the bush (i.e., taking your chances and splitting).