There are different answers to this question depending on the type of blackjack you are playing, and even then, in most cases the answers are not definitive.
The shuffle exists to ensure that the cards are in a random order and therefore that the game is fair for both the house and the player – although the house obviously has an advantage built into the rules.
The shuffle should make sure that no one knows which cards are coming up next and thus cannot be too wily in their betting behaviour.
Card counting had a big impact on the shuffle in blackjack though, and over the past few decades the way in which cards are shuffled has changed to combat this sort of advantage play.
Casinos will shuffle more often, some games utilise shuffling machines, and shoes will be swapped out more regularly in order to render an advantage players count useless.
In general though, the following will be true most of the time.
Playing Blackjack in a Casino
Plagued by professional card counters and maths geniuses using other cunning methods to beat the house, casinos changed their shuffling processes years ago to make life more difficult for anyone trying to sneak the advantage.
Using more decks per game was one way of doing this, but so was increasing the frequency of shuffles and shoe changes.
They also largely stopped offering single deck games, although you can still find them here and there if you are lucky. The way the shuffle is handled will be different if this is the case though, so we will look at single deck games separately.
Single Deck Blackjack
If you manage to find a casino willing to offer single deck blackjack you will probably find that the cards are shuffled after each couple of hands, sometimes even after each hand. Card counting is very easy when playing single deck so they will increase their shuffle rate.
Whether this is done using a shuffling machine or by hand will depend on where you are playing, although most big casinos in Europe and America now use machines.
The reason fewer casinos offer this game format is because a lot of time is wasted shuffling so often, and this is time the casino is not making money at that table. It’s all about the number of hands per hour for the casino; the more hands per hour they can achieve they more money they can statistically make.
For this reason, you will probably also find a higher minimum stake on a single deck game.
In a game using more decks of cards (usually 6 or 8), the shoe will usually be shuffled when between 40%-60% of the cards have been used.
They will employ a cut card to tell the dealer when it is time to change, and this is just a plastic card that is placed somewhere in the shoe.
The shuffle ratio depends on where you are playing and also probably the specifics of the game variant, as each house has different rules.
The shoe will either be shuffled in front of you or swapped out for one that has already been shuffled.
Casinos these days tend to use automatic machines to do this, but they know some players don’t like machine shuffling, so certain casinos will also have tables where shuffling by hand is still normal practice. This costs them because it eats into the hands per hour, but it doesn’t cost them as much as losing customers who hate shuffling machines.
Some tables even have constant shuffling machines which keep the cards shuffling all the time, meaning the game never has to stop for a shoe change or a deck shuffle.
Playing Blackjack Online
Online casinos made shuffling a thing of the past in some ways, because RNG based games do not require a dealer or real cards, the results of each deal are computer generated.
This isn’t true if you are playing at a live casino of course, so once again we need to talk about shuffling when playing online twice, coming at it from both angles.
This doesn’t actually differ too much from in a real life casino.
The tables may be in a purpose built studio and the games might be running using a combination of real cards and software, but the practicalities of game management are similar.
The shuffle is part manual part machine, and the software doesn’t know which card has been drawn until the dealer scans it once they have taken it from the shoe, so the casino and the player are in the same boat.
There are usually two shoes on each table; one in play, and another being re-shuffled. The shuffle is usually handled by another member of staff who is also on camera, and who will load the cards into an automatic shuffling machine before replacing them back in the shoe. You might find a constant shuffling machine being used by some providers, eliminating the need for shoe changes, but this isn’t common.
A plastic card is placed at a point in the shoe that is usually around mid-way through, although some providers might have it a little before or after the mid-point, and once the dealer gets to the plastic card the shoe will be swapped out.
This happens on a continuous loop, and once again the measure is in place to counter advantage players.
They will sometimes bring completely new shoes of cards to the table as well, but this happens less frequently.
RNG Based Games
For casinos, the RNG based blackjack games are a blessing, because they make it absolutely impossible to count cards.
The clever software that has been created to run these games will ‘shuffle’ the deck or shoe after each and every hand in nano seconds, so every hand is the equivalent of playing with a newly shuffled deck/shoe.
The software knows how many decks the game is using, and can work out the statistical chances of each card being drawn from there.
This is actually good news for the player in some ways too, because it is impossible for the house to implement any underhand tactics or make any costly mistakes – the games are usually run by the developer on their own network, and are just licensed out to the casinos, so the casinos themselves have no control over the outcomes.
The answer to how often the deck is shuffled when playing RNG based games then, is every single round.