When to split in blackjack
Quick answer: always split aces and eights; never split tens or fives. Nines against 2–9 except 7. Sevens, twos and threes against 2–7. Sixes against 2–6. Fours only against 5 and 6, if you can double after splitting.
The pair-splitting chart
| Pair | Split against | Otherwise… |
|---|---|---|
| A-A | all | — |
| 8-8 | all | — |
| 10-10 | never | stand |
| 9-9 | 2 through 6, 8 and 9 | stand (against 7, 10 and ace) |
| 7-7 | 2 through 7 | hit |
| 6-6 | 2 through 6 | hit |
| 5-5 | never | double against 2–9 |
| 4-4 | 5 and 6 (with double after split) | hit |
| 2-2, 3-3 | 2 through 7 | hit |
This is the 6-deck chart with doubling after splitting allowed. If your table doesn’t allow doubling after splitting, hit 2-2 and 3-3 against 2 and 3, and 4-4 and 6-6 against 2. You can see it in the interactive chart by changing that rule.
Why always aces and eights
Two aces together are worth 2 or 12, a mediocre hand. Split, each one starts on 11 and any ten turns it into 21. Two eights add up to 16, the worst hand in the game. Split, each one starts on 8. Even against a 10, splitting loses quite a bit less than playing the 16:
| Table | Stand | Hit | Double | Split | Surrender |
|---|---|---|---|---|---|
| Las Vegas (S17, surrender) | −0.538 | −0.535 | −1.070 | −0.485 | −0.500 |
| Las Vegas (H17, surrender) | −0.538 | −0.535 | −1.070 | −0.485 | −0.500 |
| Spanish casino (no hole card) | −0.573 | −0.571 | — | −0.602 | — |
Bet units per hand (−0.500 = you lose half a bet on average). Best option in green. “—”: not allowed at that table. Computed with the Veintiuno engine (6 decks unless “Double deck”), with the visible cards removed.
At a no-hole-card table, as in Spanish casinos, things change: splitting against a 10 exposes two bets to a dealer blackjack, and it becomes worse than hitting.
Why never tens or fives
A 20 is almost unbeatable. Even when the dealer shows a 6, their weakest upcard, standing on 20 is worth much more than splitting:
| Table | Stand | Hit | Double | Split | Surrender |
|---|---|---|---|---|---|
| Las Vegas (S17, surrender) | +0.703 | −0.852 | −1.704 | +0.566 | −0.500 |
Bet units per hand (−0.500 = you lose half a bet on average). Best option in green. “—”: not allowed at that table. Computed with the Veintiuno engine (6 decks unless “Double deck”), with the visible cards removed.
Something similar happens with 5-5: it’s a 10, a perfect hand for doubling down. Splitting it leaves you with two hands starting on 5.
Pairs that depend on the dealer’s upcard
The remaining pairs (2-2, 3-3, 6-6, 7-7, 9-9) are split when the dealer is weak, because two bets against a dealer who busts often are worth more than one mediocre hand. The odd case is 9-9 against a 7: you stand, because a dealer showing a 7 often ends on 17, and your 18 beats it.
| Table | Stand | Hit | Double | Split | Surrender |
|---|---|---|---|---|---|
| Las Vegas (S17, surrender) | +0.399 | −0.587 | −1.174 | +0.369 | −0.500 |
Bet units per hand (−0.500 = you lose half a bet on average). Best option in green. “—”: not allowed at that table. Computed with the Veintiuno engine (6 decks unless “Double deck”), with the visible cards removed.
Frequently asked questions
Which pairs do you always split in blackjack?
Aces and eights, against any dealer upcard, at hole-card tables. At European tables with no hole card there are two exceptions: don’t split aces against an ace, or eights against a 10 or an ace.
Should you split tens?
Never. Even against a 6, the dealer’s worst upcard, a 20 is worth +0.70 bets if you stand and +0.57 if you split. Splitting them trades a hand that’s almost won for two uncertain ones.
Should you split fives?
No. 5-5 is a 10, one of the best hands to double on. Splitting leaves you with two hands starting on 5, which are bad hands.
What about nines against a 7?
Stand. 9-9 is 18, and against a 7 the dealer often ends up on 17: your 18 wins. Standing is worth +0.40; splitting, +0.37.