When to Double Down in Blackjack
Double down on hard 11 against any dealer card except an ace, on hard 10 against 2 to 9, and on hard 9 against 3 to 6. With an ace counted as 11, double soft 13 to 18 when the dealer shows a weak card, mostly 4, 5 or 6. Never double hard 12 or more. In our simulations, doubling 11 against a dealer 6 was worth twice as much as just hitting it.
These rules are for a 6-deck game where the dealer stands on all 17s, the rules House21 uses.
What doubling down means
When you double down, you double your bet and receive exactly one more card. Then your turn ends, whatever that card is. You can only double on your first two cards; at House21 you can also double on a hand you've just split.
You give up the right to take more cards in exchange for twice the bet. That's a good trade when one card is likely to give you a strong total and the dealer is likely to finish weak.
The double down chart
| Your hand | Double against dealer | Otherwise |
|---|---|---|
| Hard 11 | 2 to 10 | Hit against an ace |
| Hard 10 | 2 to 9 | Hit |
| Hard 9 | 3 to 6 | Hit |
| Soft 13, 14 (A,2 and A,3) | 5 and 6 | Hit |
| Soft 15, 16 (A,4 and A,5) | 4 to 6 | Hit |
| Soft 17 (A,6) | 3 to 6 | Hit |
| Soft 18 (A,7) | 3 to 6 | Stand against 2, 7, 8; hit against 9, 10, ace |
| A pair of 5s | 2 to 9 | Play it as hard 10; never split |
| Hard 12 or more, hard 8 or less | Never | Follow the basic strategy chart |
Why these hands and these dealer cards
Two things make a double good.
Your next card is likely to help. Sixteen of every 52 cards are worth 10. With 11, any of them gives you 21; with 10, they give you 20. With 12, the same cards bust you.
The dealer is likely to finish weak or bust. From a 4, 5 or 6 the dealer busts about 40% of the time. From a 10 or an ace, the dealer usually reaches 17 or more, so your one-card hand needs to be strong on its own. Our bust odds tables show every dealer card.
What each double is worth
We dealt each hand against each dealer card 200,000 times and played it both ways with House21's rules. Values are the average result as a percentage of your original bet, counting hands where the dealer turns out to have blackjack. Each figure is within about ±1 point.
Hard 11 (6,5)
| Dealer shows | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | A |
|---|---|---|---|---|---|---|---|---|---|---|
| Double | +48.7% | +53.5% | +58.6% | +63.7% | +68.5% | +47.2% | +35.1% | +22.4% | +8.7% | -21.6% |
| Hit | +24.4% | +27.0% | +29.5% | +32.1% | +34.0% | +29.4% | +23.1% | +15.6% | +3.2% | -20.9% |
Hard 10 (6,4)
| Dealer shows | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | A |
|---|---|---|---|---|---|---|---|---|---|---|
| Double | +37.0% | +41.9% | +47.9% | +53.8% | +59.0% | +41.0% | +28.8% | +15.2% | -9.2% | -31.4% |
| Hit | +18.9% | +21.1% | +24.1% | +26.9% | +29.4% | +26.0% | +19.9% | +11.8% | -5.4% | -25.3% |
Hard 9 (5,4)
| Dealer shows | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | A |
|---|---|---|---|---|---|---|---|---|---|---|
| Double | +7.1% | +13.4% | +20.1% | +27.3% | +33.7% | +11.9% | -1.7% | -30.0% | -50.4% | -60.7% |
| Hit | +7.9% | +10.6% | +13.6% | +17.3% | +20.8% | +17.6% | +10.2% | -5.1% | -22.0% | -35.7% |
Soft 18 (A,7): double or stand
| Dealer shows | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|
| Double | +11.7% | +17.9% | +24.9% | +30.5% | +38.5% | +22.3% | -2.7% |
| Stand | +12.5% | +14.9% | +18.1% | +20.4% | +28.0% | +40.2% | +11.0% |
The best play is in bold. A few are close calls: 11 against an ace, 9 against a 2 and soft 18 against a 2 differ by less than a point, inside the simulation's margin. The chart follows the long-run math for these rules.
The doubles people skip
11 against a 10. It feels risky against the dealer's strongest common card. Doubling is still worth about +8.7% against +3.2% for hitting.
Soft hands. A,6 against a 4 looks like a weak 17. It's a strong double: no card can bust you, and the dealer busts about 40% of the time. Our soft 17 guide has the full table.
Soft 18 against 3 to 6. Most players stand on 18 by reflex. Against a weak dealer card, doubling it is worth 3 to 10 points more.
The doubles people get wrong
10 against a 10 or an ace. Hit instead. The dealer is too strong for a one-card hand.
Hard 12 against a 6. Tempting because the dealer is weak, but any 10-value card busts you with twice the bet out. Stand.
Doubling to chase a mission. If a daily mission asks you to win a doubled hand, wait for a double the chart recommends, like 11 against a 6. Doubling a 15 to finish it costs more than the mission pays.
Common questions
What happens if I double and lose? You lose both the original bet and the double. That's why doubling is limited to hands where you're the favorite.
Can I double for less than my original bet? Some casinos allow it, but it only makes sense if you can't afford the full amount. Correct doubles are good bets, so you want the full amount out.
Can I double after splitting? At House21, yes, on either new hand. Splitting 5s is never right, though: double them as a 10.
Why hit 11 against an ace? At these rules the dealer's ace is strong enough that doubling is slightly worse. At tables where the dealer hits soft 17, doubling 11 against an ace becomes correct.
Doubling is one of the 10 habits that cut the house edge. Practice spotting doubles at a free table in the House21 lobby.