Double Down Rules
The rules on doubling down vary from one casino to another, and some casinos will have rules that are more favorable to the player than others. Many casinos restrict when you can double down. For this reason, it is always a good idea to find out what rules are in effect before you play. With some double down rules giving the house as much as a 7 percent edge over players, it's to your advantage to do a little research and to play at casinos with less onerous rules and as few restrictions as possible.
Here are some of the rules you will see and how they can affect player expectation:
Double down only on 10 and 11. This option gives the house a 0.25 percent advantage.
Double down only on 11. This option gives the house a 0.69 percent advantage.
No soft doubling (i.e., no doubling down on hands with aces). The house gains a 0.13 percent edge with this one.
Double down only on 9, 10, or 11. This restriction is the best of them (relatively speaking), and yields a 0.10 percent advantage for the house.
Double down is allowed after pair splitting. A good rule, giving players a 0.13 percent advantage.
Double down on any two cards. This is another good opportunity for players and should be sought out.
Most casinos will only let you double down after you look at your first two cards. In other words, you can't take a hit and then say, “Geez, this is looking good. I'd better double down.” It's a nice idea, but it just doesn't happen, at least not in most gaming establishments.
However, casinos are always looking for ways to lure more players to blackjack tables, and they often jazz up the basic game of blackjack by tweaking certain rules to make conditions more favorable for players. For this reason, you will sometimes run across some interesting double down variations. In some casinos, for example, players can double down on three or more cards. In a blackjack variation game called Spanish 21, players can double on any number of cards, but the house retains its advantage by removing all 10s from the deck. Face cards, however, remain in. This simple condition change makes Spanish 21 a very good game — from the house's perspective, that is.
Allowing players to double down on more than two cards might give players a nice gain — in this case, somewhere around 0.2 percent and even a bit higher. However, this rule variation often comes at the cost of other gains, such as blackjack paying off 1 to 1. When you run across rules that have been changed to favor the player, be sure to check the other rules in place — they might be less favorable for players. As such, they can cancel the gains offered by the player-friendly rules.
With so many possible variations on double down, it can be difficult to memorize all the rules you need to know to employ this option to your best advantage. For this reason, it is a good idea to play at casinos that offer double down options that match the strategies you know. Save the more unusual offerings for later. Or consider avoiding them entirely, especially if they're decidedly adverse to players and if, when added to other rules, they give the house such a strong edge that it's barely worthwhile to go up against it.