I think casinos calculate the house edge in Blackjack by analyzing the probabilities of various outcomes and comparing them to the game's rules. The house edge represents the average percentage of each bet that the casino expects to keep over time. In Blackjack, the dealer's forced play strategy, like hitting until at least 17, gives the house a slight advantage. Casinos also factor in the payouts for Blackjack and other outcomes, as well as the probabilities of the player busting or winning under optimal conditions.