You should usually split in blackjack when you have a strong long‑term edge by turning one weak or marginal hand into two better ones, especially with pairs like aces and eights.

Core split rules (basic strategy)

Here is the widely recommended “default” for common 4–8 deck, dealer-stands- on-17 games (no special rules). Always check the exact table rules where you play.

  • Always split Aces. A pair of aces (total 12) is weak; splitting gives you two chances to make 21 with a 10-value card on each ace.
  • Always split 8s. A pair of 8s (total 16) is one of the worst totals; splitting lets you “escape” a stiff 16 and start two new hands from 8.
  • Split 2s and 3s vs dealer 2–7. Against low and medium upcards, extra money on the table tends to be favorable here.
  • Split 6s vs dealer 2–6. When the dealer shows a weak card, splitting 6s can turn one marginal hand into two competitive ones.
  • Split 7s vs dealer 2–7. The dealer is vulnerable; splitting increases your chance to win at least one, often both hands.
  • Split 9s vs dealer 2–6 and 8–9 (but not 7, 10, or Ace). Against many dealer cards, two 9s do better as separate hands than as 18, but you generally stand on 18 vs 7, 10, or Ace.

Hands you should not split

  • Never split 5s. Think of them as a strong 10; you usually want to hit or double down, not break them up.
  • Usually do not split 4s. Only some charts say to split 4s vs dealer 5–6; otherwise you play them as an 8 (often a good double-down candidate instead).
  • Do not split 10s (including face cards). A total of 20 is excellent; splitting 10s is almost always a losing long‑term move, even if it feels tempting.

Simple memory version

If you want a quick mental shortcut at the table:

  1. Always split: Aces and 8s.
  2. Often split (with conditions):
    • 2s, 3s, 6s, 7s vs dealer 2–6 (some charts extend 2s/3s/7s to dealer 7).
    • 9s vs dealer 2–6 and 8–9.
  3. Never split: 5s and 10s; usually avoid splitting 4s unless a chart specifically says 5–6.

Why dealer card matters

Splitting adds a second bet, so it is best when:

  • The dealer shows a “bust card” (4, 5, or 6) , where their bust rate jumps above 40% for some upcards.
  • Your original total is weak (like 12 or 16), so two new hands have better upside than one stiff hand.

In other words, you generally split more aggressively when the dealer is in trouble and you are starting from a bad or mid‑strength total.

Tiny basic-strategy table (HTML)

Here is a compact, beginner‑friendly view for common pairs (standard rules; may vary slightly by table):

html

<table>
  <thead>
    <tr>
      <th>Your Pair</th>
      <th>Dealer Upcard</th>
      <th>Action</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>A,A</td>
      <td>Any</td>
      <td>Split</td>
    </tr>
    <tr>
      <td>8,8</td>
      <td>Any</td>
      <td>Split</td>
    </tr>
    <tr>
      <td>2,2 or 3,3</td>
      <td>2–7</td>
      <td>Split</td>
    </tr>
    <tr>
      <td>2,2 or 3,3</td>
      <td>8–Ace</td>
      <td>Don’t split</td>
    </tr>
    <tr>
      <td>6,6</td>
      <td>2–6</td>
      <td>Split</td>
    </tr>
    <tr>
      <td>6,6</td>
      <td>7–Ace</td>
      <td>Don’t split</td>
    </tr>
    <tr>
      <td>7,7</td>
      <td>2–7</td>
      <td>Split</td>
    </tr>
    <tr>
      <td>7,7</td>
      <td>8–Ace</td>
      <td>Don’t split</td>
    </tr>
    <tr>
      <td>9,9</td>
      <td>2–6, 8–9</td>
      <td>Split</td>
    </tr>
    <tr>
      <td>9,9</td>
      <td>7, 10, Ace</td>
      <td>Don’t split (usually stand)</td>
    </tr>
    <tr>
      <td>5,5</td>
      <td>Any</td>
      <td>Never split (treat as 10)</td>
    </tr>
    <tr>
      <td>10,10 (including face cards)</td>
      <td>Any</td>
      <td>Never split</td>
    </tr>
    <tr>
      <td>4,4</td>
      <td>5–6</td>
      <td>Sometimes split (rule-dependent)</td>
    </tr>
    <tr>
      <td>4,4</td>
      <td>Other upcards</td>
      <td>Don’t split</td>
    </tr>
  </tbody>
</table>

Quick forum-style take

On blackjack forums, you will often see advice boiled down to something like:

“If you remember nothing else: always Aces and 8s, never 5s and 10s, and only get fancy with other pairs when the dealer shows a weak card. ”

That rule of thumb captures most of the value of splitting without having to memorize a full chart, and aligns closely with modern basic-strategy charts and casino training materials.

Information gathered from public forums or data available on the internet and portrayed here.