We introduce modular calculi for the logics for nonmonotonic reasoning defined by Kraus, Lehmann, and Magidor, featuring a strengthened form of analyticity. Our calculi are used to determine the computational complexity for the logics C, CL, CM, P (and M), and fragments thereof. The calculi are encoded into SMT solvers, yielding an efficient prover with countermodel generation capabilities. Our work encompasses known results and introduces new findings, including co-NP-completeness and a more effective semantics for C.