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Best of Alan Krigman

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Doubling Down Cuts House Edge in Blackjack

23 October 1995

EM>Doubling down in blackjack involves making an extra bet, equal to or less than the original wager, after seeing the dealt hand and the dealer up-card. The player then draws one and only one card. The move is beneficial when the three player and dealer cards give the bettor an edge and expected return exceeds that of hitting or standing. The accompanying table shows when the laws of probability favor doubling in multi-deck games.

Some players, including many with considerable experience, hesitate to double because of the added money at risk. When they're running scared for instance, playing with limited stakes, or watching a dealer make hand after merciless hand without breaking they may not double but hit combinations like seven-two against a dealer's four-up and stand with ace-seven against a dealer's three.

Not doubling when the opportunity arises sacrifices a chance to reduce the house advantage. But it doesn't lower the chance of winning the original bet and may even snatch a single victory from the jaws of a double defeat. Say a player hits rather than doubles on five-six against a nine-up. If the draw is six through 10, for a point total of 17 through 21, the player will stand and have the same chance of winning as on a double-down. Instead, if the draw is ace through five, the player can hit again improving the chance of winning the single bet.

Players flout the laws of probability more flagrantly by doubling when they shouldn't, because they're fighting the odds. Miracle cards can fall, yielding two whammies when one win or even a loss might otherwise have occurred. Solid citizens on a hunch under full-moon sanction have doubled on 10-eight and drawn three to beat a dealer's 10-10. But that's not gambling, it's fiscal folly.

Doubling on low starting hands is precarious because even the best possible single-card draws still leave players vulnerable. Doubling on "stiffs" like 12 or 13 is perilous because the draw can "bust" the hand. And doubling in borderline cases like nine against two, seven, or eight leaves the dealer with too great a chance to beat even a good player draw.

Experienced players often double incorrectly on "soft" hands. This most commonly occurs when the player holds ace-two or ace-three against dealer three or four, ace-four or ace-five against dealer three, and ace-two through ace-seven against dealer two. The danger is that the player's chance of drawing a strong hand with a single card is weak, while the dealer's prospects are fair-to-good.

In an eight-deck game with no resplitting, rigorous adherence to basic strategy gives the house a 0.59 percent advantage. This is equivalent to an otherwise "fair" game in which the casino levies a fee of $0.59 on every $100 bet. A player who never doubles, but follows basic strategy in other respects, would give the house a 1.37 percent bonus, more than tripling the edge to 1.96 percent or $1.96 for every $100 bet. Of the 1.37 percent, doubling on 11 accounts for 0.74 percent, 10 for 0.46 percent, nine for 0.08 percent, and appropriate soft hands for 0.09 percent.

These figures show the importance of doubling to shave the house advantage. But they also indicate that the benefit is concentrated on hands of 10 and 11. If you're concerned over risking too much money, or uncertain about when to double starting with nine or soft 13 through 18, you'll only forfeit 0.08 and 0.09 percent edge, respectively, by passing on this option with these hands. The edge is no worse than you give up by playing eight decks with no resplitting, when six-deck games are available in which you can resplit any pairs including aces.

As Sumner A Ingmark, the doubler's Dostoevski, once declared:

The quickest way a bankroll mounts,
Is putting money where it counts.

When You Should Double Down
   Player's					Dealer's up-card    Hand		2	3	4	5	6	7	8	9	T	A  Hard	9			D	D	D	D 	10		D	D	D	D	D	D	D	D 	11		D	D	D	D	D	D	D	D	D  Soft	A-2					D	D 	A-3					D	D 	A-4				D	D	D 	A-5				D	D	D 	A-6			D	D	D	D 	A-7			D	D	D	D  
Alan Krigman

Alan Krigman was a weekly syndicated newspaper gaming columnist and Editor & Publisher of Winning Ways, a monthly newsletter for casino aficionados. His columns focused on gambling probability and statistics. He passed away in October, 2013.
Alan Krigman
Alan Krigman was a weekly syndicated newspaper gaming columnist and Editor & Publisher of Winning Ways, a monthly newsletter for casino aficionados. His columns focused on gambling probability and statistics. He passed away in October, 2013.