HKSM
Early Start Date (ES)
In CPM scheduling, ES is the first moment the remaining portion of an activity is allowed to begin, determined by the schedule network relationships, the current data (status) date, and any imposed schedule constraints.
Key Points
- Calculated during the forward pass of the critical path method.
- Driven by network logic, the data/status date, and schedule constraints (e.g., SNET).
- Determines Early Finish: EF = ES + activity duration.
- On the critical path, ES equals LS because total float is zero.
Example
Activity B (3 days) has a finish-to-start relationship with Activity A. A completes at the end of day 5. The data date is day 5 and there are no constraints. The ES for B is day 6, so its EF is day 8.
PMP Example Question
Which statement best defines the Early Start Date (ES) of a schedule activity in CPM?
- The earliest time the remaining work can start, based on network logic, the data date, and any constraints.
- The latest time the activity can start without delaying the project finish.
- The actual start recorded for the activity.
- The planned start from the approved baseline.
Correct Answer: A — The earliest allowed start based on logic, status date, and constraints
Explanation: ES is computed in the forward pass using the schedule network logic, the current data/status date, and any schedule constraints to find the earliest feasible start.
