Which pairs should you always split in blackjack?

Always split aces and 8s, regardless of the dealer's up-card. Two aces are two chances at 21 instead of a clumsy 12. A pair of 8s is hard 16 — the worst hand in blackjack — and splitting turns it into two playable hands starting from 8.

Which pairs should you never split?

Never split 10s — a made 20 wins roughly four hands in five, and breaking it up costs you money against every up-card. Never split 5s either: a pair of 5s is hard 10, one of the best doubling hands in the game.

Guide · Pairs

When to Split in Blackjack

Q: Why split 8s against a 10 if both hands will probably lose?

Because losing less is winning more over time. Hitting 16 vs 10 loses about 54 cents per dollar; splitting into two hands that each start from 8 loses about 49 cents per dollar of the original bet — even after putting more money on the table. It's damage control, and it's correct.

The short version

Always split aces and 8s. Never split 10s or 5s. Split 2s, 3s, 6s, 7s, and 9s against weak dealer cards. 4s almost never. The full table is below.

Splitting is where money is made and lost in blackjack. Done right, it turns bad hands into playable ones and presses your advantage against weak dealers. Done wrong, it doubles your losses. There are only three reasons to ever split — every rule below comes from one of them.

The three reasons to split

Escape a terrible hand. 8-8 is hard 16, the worst total in the game. Two hands starting from 8 lose less.
Turn one good start into two. A-A as 12 is clumsy; as two aces, each is one card from 21. Splitting aces vs a 6 is worth +66¢ per $1 versus +19¢ for playing it as 12.
Get more money out against a weak dealer. The dealer's 4, 5, 6 bust ~40–44% of the time (the numbers). Splitting 2s, 3s, 6s, 7s there is about pressing a profitable spot.

Every pair, every up-card

Your pair	Split when dealer shows	Otherwise
A,A	Always	—
10,10	Never	Stand — 20 is a made hand
9,9	2–6, 8, 9	Stand vs 7, 10, A
8,8	Always	—
7,7	2–7	Hit vs 8+
6,6	2–6	Hit vs 7+
5,5	Never	Double vs 2–9 (it's a 10!), else hit
4,4	5, 6 only	Hit everything else
3,3	2–7	Hit vs 8+
2,2	2–7	Hit vs 8+

Assumes double after split allowed (standard in US 6-deck games). The interactive strategy chart adjusts for your exact rules.

The two pairs everyone gets wrong

9,9 vs 7 — stand (don't split)

You split 9s against 8 and 9 but stand against a 7. Why? The dealer's most likely outcome with a 7 up is exactly 17 (37% of the time) — and your 18 beats a 17. Splitting would trade a likely winner for two uncertain hands.

10,10 vs 6 — stand, every time

The most expensive "fun play" in blackjack. Yes, the dealer's 6 is weak. But your 20 already wins here at +68¢ per $1; splitting into two ten-hands drops that to about +57¢ — you're paying 11¢ per dollar to feel aggressive, twice the stake included. A made 20 wins roughly four hands in five. Keep it.

Frequently asked questions

Why split 8s against a 10 if both hands will probably lose?

Damage control. Hitting 16 vs 10 loses ~54¢ per $1; splitting loses ~49¢ per dollar of your original bet, even counting the extra money you put up. Losing less is the win. See the full 16 vs 10 breakdown.

What happens when I split aces?

Most casinos give you exactly one card on each ace, and a resulting 21 counts as 21 — not blackjack (it pays 1:1, not 3:2). Still split them every time; it's among the most profitable moves in the game.

Can I re-split if I get another pair?

Usually yes, up to 3 or 4 total hands (aces often excluded). If the first split was correct, the re-split almost always is too.

Should I split differently if doubling after split isn't allowed?

Yes, slightly — without DAS you stop splitting 2s and 3s vs 2–3, 4s entirely, and 6s vs 2. If you only memorize one chart, learn the DAS version; it's the common US rule.