To calculate the exact house edge in a blackjack game, you need to consider all the rules of the game, as well as the number of decks being used. First, you need to calculate the expected return of each hand for the player and the dealer. You can do this by multiplying the probability of each hand by the payout for that hand. Next, you need to subtract the expected return for the dealer from the expected return for the player. This will give you the player's advantage.