How does a GM calculate opening and how many moves in advance? How does a GM make his opening repertoire and how does he calculate his moves in advance.Can he calculate 20 moves in advance base on his opening?
They don't calculate the common openings, they know them by heart, at least the main lines, and the possible refutations, should the opponent deviate from the main line.

For the less common openings, they might remember things not as deep as the often playable ones. Still, it's like 10-15 plys for something obnoxious and could be as much as 20-30 plys for the most common ones.