Splitting pairs

Two rules cover most of it: always split aces and eights, never split tens or fives. The rest is the chart below.

Games › Blackjack › Splitting Pairs

Every pair, computed

H hit · S stand · D double (hit if doubling is not allowed) · P split

Your pair2345678910A
A,APPPPPPPPPP
2,2PPPPPPHHHH
3,3PPPPPPPHHH
4,4HHHPPHHHHH
5,5DDDDDDDDHH
6,6PPPPPHHHHH
7,7PPPPPPPHHH
8,8PPPPPPPPPP
9,9PPPPPSPPSS
10,10SSSSSSSSSS

The two that are always right

Split aces, always. A pair of aces is a soft 12, which is close to worthless. Split, and each ace starts a hand where any ten-valued card, four ranks in thirteen, makes 21. Most houses allow only one card per split ace, and it is still correct every time.

Split eights, always. A hard 16 is the worst total in blackjack. Two hands starting on 8 are both better than one hand of 16, even against a dealer ten. This is the split people resist most and it is not close.

The two that are always wrong

Never split tens. A hard 20 wins the large majority of the time. Breaking it into two hands of 10 trades a strong hand for two ordinary ones.

Never split fives. A pair of fives is a hard 10, one of the best doubling hands in the game. Splitting turns it into two hands starting on 5, which is the worst starting card there is.

The ones that depend

9,9 splits against most upcards but stands against 7, 10 and ace. Standing against a 7 looks odd until you notice that a dealer 7 most often makes 17, which your 18 already beats.

4,4 splits only against a 5 or 6, and only where doubling after a split is allowed. Our double after split page covers why that rule decides this hand.

2,2, 3,3, 6,6 and 7,7 split against weak dealer upcards and hit against strong ones, following the dealer bust probabilities on our dealer upcard odds page.

Frequently Asked Questions

Should I always split aces and eights?
Yes. A soft 12 and a hard 16 are both poor hands, and splitting improves each of them against every dealer upcard.
Why not split tens?
A hard 20 already wins most hands. Splitting trades one strong hand for two ordinary ones.
Why not split fives?
A pair of fives is a hard 10, one of the best doubling hands in blackjack. Double it instead.
Should I split eights against a dealer ten?
Yes. Both hands are unattractive, but two hands starting on 8 still beat one hand of hard 16.

Every figure on this page is computed by an expected-value engine that plays the game out: it derives the dealer's final-total distribution by recursion, evaluates standing, hitting, doubling and splitting at each decision, and takes the best. Rule costs are measured by re-running the whole calculation with the rule changed, not by quoting a published delta. The model assumes independent card draws, which sits a few hundredths of a percent from an exact shoe analysis; the rule differences it produces match published values. Rules vary by table, so read the felt.