Critical Path Method (CPM)

The Critical Path Method (CPM) is a project-scheduling technique that models the work as a network of activities with their durations and logical dependencies, then computes the earliest and latest start/finish of each activity by forward and backward pass. The critical path is the longest continuous chain of dependent activities — its length is the shortest possible project duration, and its activities have zero float, so any delay to a critical activity delays the whole project.

CPM is the backbone of construction programming: it identifies which activities must be protected and resourced, quantifies the float (slack) available on non-critical activities, and underpins delay analysis, extension-of-time claims and acceleration decisions. In practice the network is maintained in scheduling software, baselined in the contract programme, and progressed periodically; the critical path shifts as work progresses, so it must be re-analysed each update. It is distinct from PERT (which adds probabilistic durations) and is normally shown to stakeholders as a linked bar (Gantt) chart driven by the CPM logic.