How is the Critical Path Method (CPM) calculated?

CPM calculation involves: (1) Forward pass - calculate Early Start (ES) and Early Finish (EF) for each activity from project start (EF = ES + duration, successor ES = max predecessor EF), (2) Backward pass - calculate Late Finish (LF) and Late Start (LS) from project end backward (LS = LF - duration, predecessor LF = min successor LS), (3) Calculate Total Float (TF) = LF - EF = LS - ES, (4) Identify critical path as activities with zero float. Free Float = successor ES - own EF. CPM identifies schedule flexibility and critical activities requiring management attention.