The decision that costs money
A player who sits down at a blackjack table and splits every pair, or never splits at all, is giving away more than they need to. Splitting is the one moment in blackjack where a single hand becomes two separate wagers, each with its own outcome, and the cost of a wrong split is not a lost hand but a doubled loss on a hand that was already weak or a broken hand that was already strong.
The question underneath the query is not which pairs are good in isolation. It is which pairs are good against the specific dealer upcard showing, under the specific rules printed on the table. A pair of nines is not a fixed decision. It is a decision that changes when the dealer shows a seven, a ten, or a six.
This article walks through the mechanics of splitting, the pairs that are almost always split, the pairs that are almost never split, and the middle ground where the dealer's card and the table rules decide.
What splitting a pair does
When your first two cards are the same rank, most blackjack tables let you split them into two separate hands. You place a second wager equal to the first, and each card becomes the first card of a new hand. The dealer then deals a second card to each hand, and you play them one at a time, completing all actions on the first hand before moving to the second.
What changes after a split depends on the table rules. Some tables allow resplitting, meaning a third card of the same rank can be split again. Some allow doubling after split, some do not. Aces are usually restricted: many tables deal only one card to each split ace and do not permit resplitting them. The payout on a split hand is the same as a normal hand, but a two-card total of 21 made after splitting aces is generally paid as a regular 21, not as a blackjack at the higher 3:2 or 6:5 rate.
The strategic point is that splitting changes the composition of your hand. A pair of eights is a hard 16, one of the worst starting totals in the game. Split, it becomes two hands each starting with an eight, each with a reasonable chance to build a competitive total. A pair of tens is a hard 20, one of the best starting totals. Split, it becomes two ten-valued cards that each need another strong card to avoid becoming ordinary or worse.
How the dealer's upcard changes a split
Blackjack strategy is comparative. You are not deciding whether your hand is good in the abstract; you are deciding whether it is better than what the dealer is likely to build from the upcard showing. A dealer showing a five or a six is in a weak position because the most common card in the shoe is a ten, and a ten on a five or six produces a stiff total the dealer must hit again. A dealer showing a ten or an ace is in a strong position because the dealer may already hold a strong total or a blackjack.
The same pair can be a split against a weak upcard and a hit or a stand against a strong one. The comparison below shows the main pair types and how the decision generally breaks down, remembering that every cell assumes the specific rule set on the table in front of you.
| Pair | What you hold before splitting | Typical decision against a weak dealer upcard | Typical decision against a strong dealer upcard |
|---|---|---|---|
| Aces | Soft 12 (2 or 12) | Split | Split |
| Eights | Hard 16 | Split | Split |
| Nines | Hard 18 | Split | Stand |
| Sevens | Hard 14 | Split | Hit |
| Sixes | Hard 12 | Split | Hit |
| Fours | Hard 8 | Split only if doubling after split is allowed | Hit |
| Twos and threes | Hard 4 or 6 | Split | Hit |
| Fives | Hard 10 | Double | Double or hit |
| Tens and face cards | Hard 20 | Stand | Stand |
The table is a simplification of published basic-strategy charts, and the simplification is the point. Basic strategy is not a set of slogans. It is a decision table derived from the exact rule set in use: the number of decks, whether the dealer stands or hits on soft 17, whether doubling after splitting is permitted, whether resplitting is permitted, and how aces are treated after a split. The same pair can move from one column to another when one of those rules changes.
The pairs that are almost always split
Aces and eights are the two pairs that appear in the split column on nearly every published basic-strategy chart, regardless of the dealer's upcard. The reason is structural, not stylistic.
A pair of aces is a soft 12, which is a weak hand because any ten-valued card turns it into a 12 again, and most other cards leave it mediocre. Split, each ace becomes the first card of a hand that has a strong chance of becoming a competitive total, and even a mediocre second card leaves a soft hand that can be hit again without busting. The restriction that many tables place on split aces, one card only and no resplitting, is a recognition of how much stronger the split is than the original hand.
A pair of eights is a hard 16, which is a hand that loses more often than it wins against almost every dealer upcard. Split, each eight becomes the start of a hand that can reach 18 or better with a ten, and can be improved further with smaller cards. The split does not make the eights into a winning hand by itself; it converts one bad hand into two hands with a better expected outcome than the single bad hand, which is what a split decision is always about.
The pairs that are almost never split
Tens and face cards are the clearest example of a pair that should stay together. A hard 20 is a strong hand against every dealer upcard except an ace, and even against an ace it is a hand that wins more often than it loses. Splitting it means giving up a near-certain strong hand for two hands that each need another ten to be strong, and the probability of drawing enough tens to make both hands good is lower than the probability of winning with the 20 you already hold.
Fives are the other pair that is almost never split. A pair of fives is a hard 10, which is a strong doubling hand against many dealer upcards. Splitting it produces two hands each starting with a five, which is a weak start. The correct play with a pair of fives is usually to double the hand as a 10, not to split it into two fives.
Fours sit in a special category. A pair of fours is a hard 8, which is not a strong hand but not a disaster. The split is only attractive when the table allows doubling after splitting, because a split four that draws a five, six or seven becomes a hand worth doubling. Without that rule, the pair of fours is better played as a single hard 8.
Reading a strategy chart without memorising it
The practical skill is not remembering every cell of a chart. It is knowing what the chart is and where to find the one that matches the table you are at. A basic-strategy chart is a grid with the player's hand on one axis and the dealer's upcard on the other. Each cell contains a single instruction: hit, stand, double, split, or surrender where surrender is offered.
The chart is not a guarantee of winning any given hand. It is a map of the play that minimises the expected loss on each decision under the rule set it was built for. A chart built for a six-deck game where the dealer stands on soft 17 and doubling after splitting is allowed is not the same chart as one built for a single-deck game where the dealer hits soft 17 and doubling after splitting is not allowed. Using the wrong chart is a procedural mistake that costs money in the aggregate.
Before you play, check the table rules printed on the layout or the game information panel. The rules that matter for splitting are the number of decks, whether the dealer stands or hits on soft 17, whether doubling after splitting is allowed, whether resplitting is allowed, and whether aces receive one card only. Then use a chart that matches those rules. If you are playing online, the game information panel usually states the rule set, and the same matching principle applies.
Where the house edge sits in a split decision
Every blackjack decision, including a split, is a choice between two negative-expectation options. You are not choosing between winning and losing. You are choosing between losing less and losing more, in the long run, under the specific rule set in play. The house edge on blackjack as a whole is the mathematical advantage the operator holds on each wager, and it is the complement of the game's return to player: the two sum to 100% for the same game under the same rule set.
What a split does is change the amount wagered and the composition of the hands in play. A correct split does not remove the house edge. It reduces the expected loss on that decision relative to the alternatives. An incorrect split does the opposite: it increases the expected loss by doubling the wager on a hand that was better left alone, or by breaking a strong hand into two weaker ones.
This is why the pair of tens example matters. Splitting tens is not a neutral choice. It is a choice that increases the expected loss on a hand that was already strong, and the only reason a player makes it is a misreading of what splitting is for. Splitting is a tool for improving weak hands, not for multiplying strong ones.
Procedural mistakes that cost more than the cards
The first mistake is splitting without checking the table rules. A player who splits fours on a table where doubling after splitting is not allowed has made a play that a chart for a different rule set would not recommend. The second is splitting tens because a strong hand feels like a chance to win twice. It is a chance to lose twice on two hands that are each weaker than the hand already held.
The third mistake is treating a split as a way to recover losses. A split doubles the wager on the hand in front of you, and a player who is splitting more aggressively because they are behind is increasing the amount at risk on decisions that are already negative-expectation. The split decision should be made on the cards and the dealer's upcard, not on the state of the session.
The fourth is touching the cards or moving chips in a way that is unclear to the dealer. In a hand-dealt game, the standard procedure is to place the second wager next to the first and point with one finger, or to make the split gesture the table expects. The dealer handles the cards. In an online game, the split button appears when a split is available, and the second wager is deducted when you press it. The procedural rule is the same: make the intention clear before the cards are dealt.
FAQ
Is it ever correct to split tens in blackjack?
Published basic-strategy charts almost never recommend splitting tens, because a hard 20 is a strong hand and the split produces two weaker hands. The only contexts where a split of tens appears in some advanced discussions are highly specific card-counting situations, which are outside basic strategy and depend on the exact count and rule set.
Why are aces and eights always split?
Aces and eights are split because the original hand is weak and the split hands have a better expected outcome. A soft 12 and a hard 16 are both poor starting totals, and splitting them converts one poor hand into two hands with a better chance of becoming competitive, which is why the split appears across most rule sets.
Does the number of decks change which pairs to split?
It can. The number of decks changes the probabilities of drawing certain cards, and a chart built for a single-deck game can differ from one built for a six-deck or eight-deck game. The rule set as a whole, including deck count, dealer soft-17 rule, and doubling after splitting, determines which chart applies to the table you are at.
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This article is general information about how these mechanics work. It is not legal advice and not a recommendation to gamble or to use any particular operator. Availability and legality differ by jurisdiction — check the rules that apply where you are.