23 Nov

# Is It Ever Correct to Double on Natural Blackjack?

Exploratory Strategy: Double Down on Natural Blackjack?

The other night, a few friends and I met up at the local casino. We planned to spend a few hours at the blackjack tables before hitting up the buffet for dinner; (assuming we had any money left). It was a good evening. None of us lost our wallets, but only my friend (we’ll call them J.D.) came out ahead. Then, as we got to our dinner table, a very interesting conversation ensued…

My other friend, I’ll call them B.B., had the worst night between us, posed the following question: “Is it ever a good idea to double on natural blackjack?

After asking him to restate the query—surely I’d misunderstood—I was taken aback. Truly? Should you take another card after being dealt a two-card total of 21? Was this a joke? No, it was not. In fact, his friend had heard a few weeks prior that it was the right move, in the right circumstances.

## Double Down on Natural Blackjack: The Theory

B.B proceeds to tell us that doubling is a good move—nay, the strategically proper move—if the following criteria exists.

1. The game must be 6:5 Blackjack.

2. The dealer’s face-up card must be a 4, 5 or 6.

## Exploring the Blackjack Doubling Strategy

At this point, it was at least worth considering the concept. As he B.B. quick to point out, in 6:5 Blackjack games, a two-card 21 will only pay \$12 for a \$10 bet; not the traditional 3:2 payout of \$15 for \$10. Therefore, the guaranteed blackjack win would pay \$12, while winning on the double down—guaranteed not to bust the player—would deliver a \$20 payout. That’s a notable increase of 40% in winnings.

Secondly, the dealer’s odds of busting on a 4, 5 or 6 are the highest in the game. With a face-up 4, the dealer is looking at a 40.28% bust rate; on a 5 it’s 42.89%, and on a 6, it’s 42.08%. These are the only cards with an above 40% chance to bust the dealer. Average them all together, and that’s a 41.75% bust rate on dealer showing 4, 5 or 6.

## The Problem with Doubling on Blackjack

As B.B. was quick to learn, this is a very bad idea. I can give you several very good reasons why you should never double on natural blackjack. First and foremost, there is no guarantee you will win the bet. The only guarantee is that you will not bust. Let’s look at the possibilities…

At worst, you are dealt anything from Ace to 5, delivering an abysmal hand total of 12-16. Let’s remember there’s a 41.75% chance the dealer will bust, which leaves a garish 58.25% chance the dealer will not bust. Add to that a 40.82% this is what you’ll receive if the dealer has a 6 showing; or 38.79% with dealer showing 4 or 5.

Almost as bad, you could be dealt a 6, giving you a total of 17 (6-8% chance). This hand might push, but cannot possibly win unless the dealer busts. The odds of any above scenarios happening are 44.9%.

At best, you receive a 10 / face card, bringing your total back to 21. With this, you are likely to win, but could still push on a tie. The odds of being dealt a 10/face card are 30.61%.

The odds of any other card coming—cards that could just as easily win, lose or push—are 24.49%.

Essentially, to double down on natural blackjack is to take a hand with a 100% win rate and toss it away for a variable win/loss/tie rate. Even if your odds of winning are higher overall than your odds of losing, giving up a 100% guarantee is just plain ludicrous!