Lag and Lead: Critical Schedule Adjustments for the Exam

PMBOK v8 Definition

A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor activity. A lag is the amount of time whereby a successor activity will be delayed with respect to a predecessor activity. In scheduling software, a lead is often represented as a negative value for lag. These concepts are applied within the Schedule Management knowledge area during the Develop Schedule process.

Why It Matters for the Exam

The PMI exam frequently tests your ability to distinguish between lead and lag, as they are commonly confused yet fundamentally opposite concepts. Questions appear in both definition-based and application-based formats, often requiring you to identify which adjustment is appropriate for a given project scenario or to interpret how a lead/lag affects a finish-to-start (FS) dependency.

Key Points to Remember (for the exam)

Lead Definition: Time a successor activity can be advanced relative to its predecessor (e.g., starting landscaping 2 weeks before punch list completion = FS + 2-week lead).
Lag Definition: Time a successor activity will be delayed relative to its predecessor (e.g., starting editing 15 days after writing begins = SS + 15-day lag).
Negative Representation: In scheduling software, a lead is entered as a negative value for lag (e.g., a 2-week lead = -2 weeks lag).
Common Dependency Type: Lead and lag are most frequently applied to finish-to-start (FS) relationships, but can apply to any dependency type.
Exam Trap Trigger: Watch for questions that describe a delay (lag) but use the word "advance" or vice versa—read the scenario carefully.
Real-World Example from PMBOK: Technical writing team begins editing draft 15 days after they begin writing = SS with a 15-day lag.

Typical PMI Exam Example

A construction project has a finish-to-start dependency between "Complete Punch List" and "Landscape Building Lot." The landscape contractor can begin work 2 weeks before the punch list is fully complete. What schedule adjustment should the project manager apply?

Answer: Apply a 2-week lead to the successor activity (Landscape Building Lot), which is represented as -2 weeks lag in scheduling software.

PMI Exam Traps

Trap: Confusing lead with lag by focusing on the word "advance" vs "delay" without reading the full scenario. Reality: Lead = successor can start earlier (advance); Lag = successor must start later (delay).
Trap: Assuming lead and lag only apply to finish-to-start (FS) dependencies. Reality: Lead and lag can be applied to any dependency type (FS, FF, SS, SF).
Trap: Thinking a lead is always a positive number and lag is always negative. Reality: In scheduling software, lead is entered as a negative value for lag. A 2-week lead = -2 weeks lag.
Trap: Misinterpreting a scenario where work overlaps (lead) as a different dependency type. Reality: Overlapping activities with a dependency still use the same dependency type—only the lead/lag adjustment changes.

Important PMI Connections

Related Concept	Relationship Type	Exam Attention Point
Schedule Network Analysis	Tool/Technique used within	Lead/lag are adjustments applied during network analysis to reflect realistic timing
Dependency Determination	Complementary concept	Lead/lag modify the timing of established dependencies (FS, FF, SS, SF)
Develop Schedule	Process where applied	Lead/lag are inputs to schedule development; tested as tools for schedule compression or realistic modeling
Schedule Compression	Related technique	Applying leads can compress schedule (fast tracking); lags typically extend schedule
Critical Path Method	Related calculation	Lead/lag adjustments affect the critical path calculation and total float

Quick Review Questions

A project team determines that the testing activity can begin 5 days after the coding activity starts. What schedule adjustment is this, and what dependency type is most likely used?
In scheduling software, how is a 3-week lead represented in terms of lag value?
A successor activity with a finish-to-start dependency has a 10-day lag applied. Does the successor start earlier or later than the predecessor's finish?
A project manager wants to overlap the "Design Review" and "Documentation" activities. The team decides documentation can begin 1 week before design review finishes. What adjustment is needed?
True or False: Lead and lag can only be applied to finish-to-start (FS) dependencies.

PMBOK v8 Reference

Section 5 – Tools and Techniques (pages 179-180) Figure 5-12 – Examples of Lead and Lag