The question a split answers
When your first two cards match in value, you may usually place a second bet equal to the first and play two separate hands. Each hand starts with one of the original cards. The question is whether two hands starting from that card are, on average, worth more than one hand starting from the pair’s combined total.
Because a split puts more money at risk, the answer has to be better by enough to justify the second bet. This article sorts the pairs into groups. The most important two are covered in more depth in the piece on splitting aces and eights, and the case against splitting tens has its own article.
Group one: always split
Aces and eights are split against every dealer upcard in standard basic strategy, with some rule-dependent exceptions (for example, when the dealer hits soft 17 or when surrender is available, a few charts treat eights against an ace differently).
- A pair of aces is a hard 12 if kept together, which is poor. Split, each ace starts a hand with a strong chance of reaching 21 or close to it.
- A pair of eights is a hard 16, the worst total against most upcards. Split, each eight starts a hand at 8 that can be improved.
In both cases the pair as a whole is worse than the sum of its parts.
Group two: never split
Tens and fives are not split.
- A pair of tens is a hard 20, one of the best hands in the game. Splitting trades it for two hands beginning at 10, each a good start but not as good as a made 20.
- A pair of fives is a hard 10, a hand you would normally double against most upcards. Splitting turns it into two hands starting at 5, which is a weak start. Doubling is the better use.
You can check the sums: 5 + 5 = 10, which is a strong doubling total, while a hand starting at 5 has a lot of work to do. Likewise 10 + 10 = 20.
Group three: split against weak dealer cards
For most of the remaining pairs the rule is the same shape: split when the dealer is weak, play the total otherwise. The reasoning is that a weak dealer, one likely to bust, makes it worth putting a second bet on a hand that begins from a modest card.
- Twos and threes: split against dealer 4 through 7, and also against 2 and 3 when doubling after a split is allowed. Kept together, they make a hard 4 or 6, which is a poor total, so splitting starts two hands that are no worse and put more money out against a vulnerable dealer.
- Sixes: split against 2 through 6 (the 2 depending on the rules). A pair of sixes is a hard 12, which is a stiff hand that can bust easily. Splitting gives two hands beginning at 6.
- Sevens: split against 2 through 7. A pair of sevens is a hard 14, which is a weak total against any dealer card.
- Nines: split against 2 through 6, 8 and 9, and stand against 7, 10 and ace. A pair of nines is an 18, a good hand, so splitting makes sense only when the dealer is weak (2 to 6) or when 18 is not enough to beat the likely dealer total (8 or 9). Against a 7, an 18 usually already beats the dealer’s most likely 17, so you stand. Against a 10 or ace, splitting would double your exposure to a strong dealer.
- Fours: usually played as a hard 8 and hit. A few charts split them against a 5 or 6 when doubling after a split is allowed, as covered by the rule variations.
Notice that nines break the pattern slightly. That is the reason they are worth reviewing separately when you work on memorising strategy.
Why the rules about doubling after a split matter
Whether you may double down on the new hands after splitting changes the value of splitting smaller pairs. If it is allowed, a hand that starts at 2 or 3 and then draws to 9, 10 or 11 can be doubled, which makes the split worth more. That is why twos, threes, fours and sixes split in a wider range of upcards with that rule. Limits on resplitting, and the special restrictions on split aces at some tables, also change the value, a topic covered in the resplit limits article.
A simple illustration
Take a pair of eights against a dealer 10, and a bet of 10 units. This is deliberately an illustration of the idea, not a table of exact values.
- Kept together, you hold a hard 16 against a strong card, one of the worst situations in the game. Both hitting and standing tend to lose more often than they win.
- Split, you bet another 10 units, so 20 units are now at risk, but each hand begins from 8 and can reach a decent total.
Splitting is not good in the sense of winning more than losing. It is better in the sense of losing less on average than the alternatives. Basic strategy can be a damage-limiting decision as much as a profitable one.
Limits of the guidance
Splitting means more money on the table and higher swings. Following the chart will not stop losing sessions, and the house edge still applies. Past hands do not affect future ones. If gambling is causing problems, contact a local support service.