The rules for feeder and service load calculations differ from those for branch-circuit calculations. Do you know the differences?
With branch circuits (Art. 220, Part II), you’re basically determining what the various loads will be for a given structure. That is, X amount of lighting load, X amount of receptacle load, X amount of specific loads based on the occupancy or some other factor.
But you size each of your feeders based on the sum of the branch-circuit loads