In most cases the house rules on blackjack will only allow players to double down on two starting hands: a hard 10 and a hard 11. But if you look at a basic strategy chart you’ll see that there are more recommended times to double then only when you have a hard 10 or hard 11.
Limiting when a player can double down in blackjack is the casinos’ way of trying to take away some of the effectiveness of an advantageous play. Doubling down at the most opportune times will hit the house’s edge for 1.6%. This is why doubling down is the most advantageous play in a blackjack player’s arsenal. By limiting when this play can be made, casinos are taking away from its effectiveness.
In other words, casinos don’t like that players can hit their house edge that hard and improve their odds, so they will do what they can to turn the tables.
This even applies to online blackjack. Online blackjack games are already programmed so that players don’t have the opportunity to double down on every hand. This is good for the online casinos because it keeps players from making extra on every hand they win. But it’s also good for players because it limits the losses that could happen from players who would become double down happy.
However some online blackjack games are just as limited as a brick-and-mortar casino in that they only allow double downs on hard 10s and hard 11s.
Going back to brick-and-mortar casinos, some will allow players to double down with more hands than just a hard 10 or hard 11. Take a look at your basic strategy chart again. You will see there are a good number of soft hands that are advantageous to double down on too.
By playing at table that allows players to double down on any hand, blackjack players can take advantage of those soft hand double downs too. The best soft hands to double down on are any in which you’re facing a dealer’s 6. Unless you have a soft 20, and in that case your best play is to stand—don’t throw a good hand away.
Always be on the lookout for a blackjack table that lets you double down on any two cards. And if you’re playing blackjack online and find a game that will only let your double down on a hard 10 or hard 11 find another online blackjack game to play.