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Best of Alan Krigman

Gaming Guru

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Doubling Down in Blackjack Can Give the Player an Edge

5 December 1994

ou're the underdog almost every time you bet in a casino. Almost. A few wagers give you the advantage.

The casino gets its edge on most bets by paying less than what's dictated by your chances of winning. Place $5 on the four at craps, for instance. You're fighting 2-to-1 odds so a "fair" bet would pay $10. Instead, you win $9. The difference is the commission the casino takes on your action to help finance the world-class adult leisure mecca in which it allows you to gamble.

The rake off the top may seem small, but play enough and it can build to big bucks. So shrewd players grab whatever opportunities arise for wagers where the house gets little or no cut. Or where the bettor has the edge.

"Doubling down" in blackjack is the most common way you can get the best of it. After seeing your own first two and the dealer's single exposed cards, you can make a second bet as high as your initial wager, then draw once. Doubling on the right hands gives you the edge because the new bet pays even money although it's made knowing that you're favored to win.

Rules about when to double vary slightly depending on the specifics of the game being played. Here's a set for six- or eight-deck games in which you're allowed to double on any two cards.

Player Dealer
Hard 11 (9-2, 8-3, 7-4, 6-5) 2 - 10
Hard 10 (8-2, 7-3, 6-4, 5-5) 2 - 9
Hard 9 (7-2, 6-3, 5-4) 3 - 6
Soft 18 (A-7) 3 - 6
Soft 17 (A-6) 3 - 6
Soft 16 (A-5) 4 - 6
Soft 15 (A-4) 4 - 6
Soft 14 (A-3) 5 - 6
Soft 13 (A-2) 5 - 6

Some doubles give you substantial advantage. As examples:

Double on 11 against dealer six. Probabilities are you'll win 63.3, tie 6.7, and lose 30 percent. Play this hand for $10 a thousand times and expect to win $6330 and lose $3000 for a net profit of $3330 on the extra bet alone.

Double on 10 against dealer five. Probabilities are you'll win 59.3, tie 7.1, and lose 33.6 percent. After a thousand such $10 doubles, expected net profit on the extra bet is $5930-$3360=$2570.

Other cases offer you smaller advantages, but the move is still attractive. To illustrate:

Double on nine against dealer three. Probabilities are you'll win 49.6, tie 6.8, and lose 43.6 percent. Expected profit on the extra bet after a thousand $10 doubles on this hand is $4960-$4360=$600.

Doubling on the wrong hands gives the house an edge, so the extra bet wastes money. Say you double on eight against dealer seven. Probabilities are you'll win 41.5, tie 7.7, and lose 50.8 percent. A thousand of these at $10 can be expected to lose $5080-$4150=$930 on the extra bet. Combine this with the loss on the initial bet, and recognize that had you hit, the original $10 has an expected net profit of over $800 on the thousand hands, to see the true cost of the error. Likewise, all doubles on or below totals of seven are losers.

Some solid citizens don't double, fearing dents that losing the extra bets might make in their bankrolls. But if this is why they sweat the best wagers in town, they're betting too high in the first place. It's wiser to start lower and be positioned to exploit opportunities like doubling on favorable hands. As Sumner A Ingmark, Tennyson of the tables, so truthfully testified:

A blackjack player is in trouble
If he ignores the chance to double.
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.