Splitting fives in blackjack

3 March 2016

By John Grochowski

For basic strategy players in blackjack, there are a few absolutes when pairs are dealt:

• Always split aces and 8s.


• Never split 5s or 10s.

What brings this to mind as I write is an e-mail exchange with a reader who ignores one of the absolutes. He likes to split 5s, and I don’t seem likely to convince him to change his ways.
More on that in a minute. First, let’s take a brief look at the absolutes.

There’s a minor qualifier on the splitting 8s rule: If the dealer hits soft 17 in a multi-deck game and you’re in one of the rare casinos that offer surrender, then it’s best to surrender 8-8 instead of splitting if the dealer has an ace face-up. And absolutes can add “never split 4s” in games where you’re not permitted to double down after splitting.

The admonitions against splitting 5s or 10s are so strong that basic strategy tables at wizardofodds.com don’t list those hands at all. You always stand on 10-10, and you play 5-5 just like any other 10. Don’t even think about splitting.

Still, there are players who ignore the absolutes. There are those who split 10s – usually to the groans of other players and a call of “Splitting 10s!” from the dealer to the pit supervisors. With two 10s, your starting hand of 20 is so strong that you’ll make more money by standing than you will by making a extra bet to turn it into two starting hands of 10 each.

It’s rarer to see someone split 5s. The temptation isn’t as strong because most players recognize 5 as a weak building block for a hand, while 10 is a strong one. When the dealer has 5 up, we stand on our weaker hands and double down on some of our stronger ones, and let the dealer take a chance on going bust. Why would we intentionally give ourselves that weak start?

Not only that. If the dealer has a low card face up and we see ourselves as having an edge, there’s a better way to press home our advantage. Double down on any dealer face-up cards except 10 or ace, and you have a better investment than splitting the pair.

Let’s compare expected outcomes for our six-deck game if you have 5-5 and the dealer has 6 face-up.

• If you double down, your expected profit per $1 of your original wager is 58.8 cents.


• If you just hit, that expected profit is 29.4 cents.


• If you split, the expected profit is 10.4 cents.

The weakness of starting a hand with 5 shows in decreased profit when you split the pair even when the dealer has a weak card face-up. We make nearly six times as much money without any more risk when we double down instead of splitting. Just hitting isn’t the optimal play, but it brings nearly three times the return of splitting with less money risk.

The e-mailer who started this discussion told me he likes the idea of getting a third bet on the table if he’s dealt another 5, that the play has been profitable for several years, and that when dealing himself hands and home, splitting looked like his best option.

I’m not going to convince him, and that happens. Nonetheless, the best play for a pair of 5s is to double down against 2 through 9, and stand against 10 or ace. It is not a close call.

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