When to Double Down in Blackjack

Which hands to double, which to hit, and the numbers behind it.

Basic strategy says

Double 11 against 2 to 10, 10 against 2 to 9, 9 against 3 to 6

Doubling means you double your bet and take exactly one more card. It is the right play when your hand is strong enough that the extra money is likely to be well spent, which is mostly hard 9, 10 and 11 against a weak dealer card.

When to double on hard 9, 10 and 11

Here are the rows for hard 9, 10 and 11 from the basic strategy chart. Dealer stands on soft 17, surrender not allowed, double after split allowed.

	2	3	4	5	6	7	8	9	10	A
9	H	D	D	D	D	H	H	H	H	H
10	D	D	D	D	D	D	D	D	H	H
11	D	D	D	D	D	D	D	D	D	H

H HitS StandD Double (else hit) · Ds Double (else stand)P SplitR Surrender (else hit; 17 v A else stand; 8,8 v A else split)

A D means double. Where doubling is not allowed (for example, after you have already taken a card), take a hit instead. Against an ace, 11 is a hit when the dealer stands on soft 17 and a double when the dealer hits soft 17. See dealer hits or stands on soft 17.

The numbers: why 11 is the best double

These are the average results per £1 of your original bet on a hard 11. Doubling puts two bets out, so the figures show what you expect to win or lose on the original £1. They assume an infinite deck and a dealer who checks for blackjack, and they are calculated exactly, not simulated.

Dealer card	Double	Hit	Best play
2	('+£0.471',)	+£0.238	Double
3	('+£0.518',)	+£0.260	Double
4	('+£0.566',)	+£0.283	Double
5	('+£0.615',)	+£0.307	Double
6	('+£0.667',)	+£0.334	Double
7	('+£0.463',)	+£0.292	Double
8	('+£0.351',)	+£0.230	Double
9	('+£0.228',)	+£0.158	Double
10	('+£0.089',)	+£0.033	Double
A	−£0.232	('−£0.209',)	Hit

Against a dealer 6, doubling an 11 wins about 66.7 pence per £1 on average, against 33.4 pence for just hitting. Doubling roughly doubles the profit on a hand you are favourite to win. Against a 10 the edge is smaller, about 8.9 pence, but doubling is still better than hitting. Against an ace, hitting is better by about 2.3 pence per £1 when the dealer stands on soft 17.

Why these hands

An 11 turns into 21 whenever the next card is a 10, jack, queen or king, which happens about 31% of the time, and most other cards give you a strong total of 17 to 20 or better. You can never bust on one card, so you risk very little by taking one card with more money out. A 10 works the same way, one card behind. A 9 only doubles against a dealer 3 to 6, where the dealer is weakest.

Hard 12 to 16 are not doubled. Any card from 6 upwards busts them, so the extra bet is more likely to be lost than won.

Close calls

A few doubles are close. They are worth knowing because tables with different rules shift them.

Hand against dealer	Double	Hit	Best play
Hard 9 against 2	+£0.061	('+£0.074',)	Hit
Hard 9 against 3	('+£0.121',)	+£0.101	Double
Hard 10 against 9	('+£0.144',)	+£0.117	Double
Hard 10 against 10	−£0.085	('−£0.054',)	Hit
Hard 11 against ace (dealer stands on soft 17)	−£0.232	('−£0.209',)	Hit
Hard 11 against ace (dealer hits soft 17)	('−£0.236',)	−£0.237	Double

Soft hands such as ace-6 and ace-7 are also doubled against some dealer cards. See soft hands strategy and soft 18.

Other things to know

Check what your game allows. Some tables only let you double on 9, 10 or 11, or not after a split. Set the rules in the blackjack calculator.
You only get one card. After doubling you cannot hit again. A double on 11 that draws a 2 leaves you on 13, and that is part of the maths above.
Doubling after a split is often allowed and makes splitting slightly better. See when to split pairs.

More blackjack strategy guides

Blackjack basic strategy chartA printable chart for hard totals, soft totals and pairs that changes with your table rules.16 against a dealer 10Hit, stand or surrender? The numbers behind blackjack's most famous decision.Soft hands strategyHow to play soft 13 to soft 20, such as ace and 7 or ace and 6.Soft 18 (ace-7)Stand, hit or double? The hand that is most often played wrong.When to split pairsWhich pairs to split against each dealer card, and which never to split.Should you split 9s?Split against some dealer cards, stand against others, and why.When to surrenderThe few hands where giving up half your bet is the best move.Dealer hits or stands on soft 17What the rule changes and which plays are different.Blackjack insuranceWhy the side bet loses money, and what even money means.Blackjack house edgeHow much the casino wins, and how much each rule changes it.

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Frequently asked questions

When should I double down in blackjack?

Double hard 11 against a dealer 2 to 10, hard 10 against a dealer 2 to 9 and hard 9 against a dealer 3 to 6. Against an ace, double 11 only if the dealer hits soft 17. Some soft hands are doubled too, such as ace-6 against a 3 to 6.

Should I double down on 11 against a dealer 10?

Yes. It is closer than the smaller dealer cards, but doubling wins about 8.9 pence per £1 on average against about 3.3 pence for hitting.

Should I double down on 10 against a dealer 10?

No. Hit instead. Doubling 10 against a 10 loses about 8.5 pence per £1 on average, while hitting loses about 5.4 pence.

Why not double on 12 or 13?

Those hands bust on many cards. Doubling means a bigger bet on a hand that busts more often than it wins.

What if my game does not allow doubling?

Take a hit instead. The calculator shows the fallback, such as Double (else hit), when doubling is the best move but may not be allowed.