Splitting
The second option to increase your original wager is known as “splitting”. When you receive two cards of the same value, you are allowed to match your original bet, and split the two cards into separate hands. You are not required to split; you can play the hand like any other hand, but in some situations, it is advantageous to make two hands out of a pair. It is entirely up to you.
Each card of the pair becomes the first card of a separate, totally independent, hand, and each wager - the original bet and the second bet - applies only to the hand to which it is attached. The dealer gives one additional card on the first hand, and then takes instructions on additional hits. When that hand is completed, the second hand proceeds in the same manner.
Since the two hands are independent, you may win both, lose both or win one and lose one. To split a hand, place an identical bet next to your original bet. The wager must be the exact amount; it cannot be any more or any less.
Depending upon the rules of the individual casino, you may be able to split hands up to four times. For example, if you have two Eights, split them, and receive a third Eight, you may split that hand to make three independent hands. The rules concerning how many times you may split vary from casino to casino.
The only card that has different splitting rules is the Ace. When you receive two Aces and split them, you only receive one card on each Ace. If that card is a ten-value card, it is simply a count of 21, not a blackjack, which must appear in the first two original cards.
In many casinos, you may also double down after splitting. The same rules apply for doubling down on a split hand as would for an original hand.