The approach
The critical path is the longest duration chain through a valid dependency network under the schedule’s assumptions. It can change as durations and logic change.
- List activities, their durations and genuine finish/start dependencies.
- Calculate earliest start and finish through the network, then compare complete paths.
- Check resource constraints and calendars, and revisit the controlling path after changes.
Worked example
A service rollout has preparation A (3 days), followed by parallel configuration B (5 days) and training preparation C (2 days). Acceptance D (4 days) waits for both. A–B–D takes 12 days; A–C–D takes 9 days. Earliest finish is 12 days if resources permit the parallel work.
Limits & next steps
The example assumes finish-to-start links, no lags and sufficient resources. A path calculation alone does not establish a feasible staffing plan.
Source & further reading
This explanation and worked example are independently written. The linked publication provides context for the technique; it is not a licence to reuse its material.