HKSM
Lag
A planned waiting period that delays the start or finish of a successor activity relative to its predecessor in a dependency link.
Key Points
- Lag is a delay applied to the relationship between activities (FS, SS, FF, SF), not to the activities themselves.
- It is usually a positive duration that postpones the successor; a negative value would represent a lead (accelerating the successor).
- It models non-work waiting time such as curing, drying, shipping, or approval wait periods.
- Defined in the schedule network as a duration or time unit on the dependency link and does not consume resources.
Example
Activity A: Pour concrete. Activity B: Strip forms. The relationship is Finish-to-Start with a 2-day lag to allow the concrete to cure. B cannot start until 2 days after A finishes.
PMP Example Question
A schedule shows Activity B cannot start until three days after Activity A finishes, even though A is complete. What is this three-day period called?
- Lead
- Float
- Lag
- Management reserve
Correct Answer: C — a planned delay between a predecessor and its successor
Explanation: Lag is the intentional waiting time inserted on a dependency link; lead accelerates the successor, float is schedule flexibility, and reserves are contingency buffers.
