Blackjack deviation is a term used in the game of blackjack to describe the difference between the theoretical odds of winning and the actual odds of winning for a given hand. For example, if a player is dealt a hand with an expected value (EV) of 10, but their actual experience indicates that they are likely to win only 9.5 times out of every 10 hands, their deviation would be +0.5 (10-9.
5=0.5). Deviation can be positive or negative, and can range from very small amounts up to significant percentages.
Deviation is important because it allows casinos to set different betting limits for hands with high versus low deviations. For example, if a hand has a low deviation but is expected to win only 60% of the time, the casino might only allow players to bet 1/2 their total bankroll on that hand, while they would allow players to bet full bankrolls on hands with a higher deviation if they are more likely to win.
While deviation is an important factor in blackjack, it is not the only factor that determines how players will fare at a casino. In fact, some players might even argue that deviation is not even an important factor at all! Instead, it seems that player skill and card-playing intuition are much more important factors when it comes to winning at blackjack.
