You should double down in blackjack when your starting hand and the dealer’s upcard give you a strong mathematical edge, typically with totals of 9–11 against a weak dealer card, plus certain “soft” hands with an ace.

What “double down” means

  • Doubling down means you double your original bet after your first two cards and take exactly one more card, then you must stand.
  • You can usually only do this immediately after the initial deal, before you hit or stand normally.

Classic basic-strategy spots

In standard blackjack (multiple decks, dealer stands on soft 17, doubling allowed on any two cards), common basic-strategy recommendations include:

  • Total of 11
    • Double down against any dealer card except an ace in many charts; some guides say double against all upcards, others advise just hitting vs ace depending on house rules.
* Reason: Any 10-value card gives you 21, and there are more 10-value cards than any other value.
  • Total of 10
    • Double down when the dealer shows 2–9, and usually just hit if the dealer shows 10 or ace.
* Your chance of making 19 or 20 is strong while the dealer is not in a dominant position.
  • Total of 9
    • Double down when the dealer shows 3–6 (sometimes 2–6 depending on the exact chart); otherwise hit.
* These dealer cards are considered “weak,” with higher bust probabilities.

Soft-hand doubling (hands with an ace)

Soft hands include an ace counted as 11 (for example, A–6 = soft 17). Common recommendations:

  • Soft 16–18 (A–5, A–6, A–7)
    • Often double down against dealer 4–6, because the dealer is weak and you can improve safely with one card.
* If the dealer shows a higher card, basic strategy usually prefers hitting or standing instead of doubling.
  • Very weak soft hands (A–2, A–3)
    • Generally not good double-down candidates unless rules are very specific and dealer is extremely weak; many guides suggest just hitting.

When you should not double down

  • When your total is higher than 11 and you risk busting with one card (for example 12–16), doubling usually increases losses.
  • When the dealer shows strong upcards (10, face card, or ace), most strategies recommend playing more conservatively and avoiding doubles except in a few very specific count-based or advanced scenarios.
  • Doubling with weak soft hands (like A–2, A–3) is generally avoided unless the dealer’s card and table rules make it unusually profitable.

Quick mental checklist at the table

  • Ask: “Do I have 9, 10, or 11?”
    • If 11: likely double (except sometimes vs ace, depending on rules).
* If 10: double vs dealer 2–9.

* If 9: double vs dealer 3–6.
  • Ask: “Do I have a soft 16–18 and the dealer shows 4–6?”
    • If yes, that is often a double-down opportunity.

Remember that exact “correct” plays can change with house rules (number of decks, whether dealer hits soft 17, whether you can double after split), so a basic-strategy chart for your specific game is the best reference.

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