Lag and Lead Time in Primavera P6.

Introduction

In Primavera P6, Lag and Lead times are mechanisms used to adjust the timing between predecessor and successor activities. These adjustments help control the delay or overlap between activities, offering flexibility in scheduling.

Lag refers to a delay or waiting period between activities.
Lead refers to an overlap or acceleration between activities, effectively allowing the successor activity to start or finish before its predecessor.

Both lag and lead can be applied to any type of activity relationship (Finish-to-Start, Start-to-Start, Finish-to-Finish, Start-to-Finish), and they are essential tools for fine-tuning project schedules to optimize timelines.

Lag Time

Lag is the delay between the start or finish of a predecessor activity and the start or finish of the successor activity. It pushes the start or finish of the successor activity forward in time.

Key Characteristics of Lag:

Positive Value: Lag is always a positive value, representing a waiting time between two activities.
Increases Schedule Duration: When lag is applied, it extends the time between activities, lengthening the project schedule.
Can Be Used in All Relationships: Lag can be applied to Finish-to-Start (FS), Start-to-Start (SS), Finish-to-Finish (FF), and Start-to-Finish (SF) relationships.

Examples of Lag Time:

Example 1: Construction Project (Finish-to-Start with Lag)

Predecessor Activity: Complete foundation work.
Successor Activity: Start framing the structure.
Lag: 3 days.

In this example, after the foundation work is completed, you need a 3-day waiting period (lag) to allow the concrete to cure before framing can start. The lag ensures that the successor task is delayed for 3 days after the predecessor finishes.

Example 2: Software Development (Start-to-Start with Lag)

Predecessor Activity: Start designing the software architecture.
Successor Activity: Start coding the software.
Lag: 5 days.

The design team can start coding only after the software architecture design has progressed for 5 days. This lag allows enough time for the architectural structure to be well-defined before coding begins.

Lead Time

Lead is the overlap between two activities, allowing the successor to start or finish before the predecessor is fully completed. It’s often referred to as negative lag since it accelerates the timing between the two activities.

Key Characteristics of Lead:

Negative Lag: Lead is applied as a negative value to introduce an overlap.
Reduces Schedule Duration: Lead helps shorten the overall project schedule by allowing activities to overlap or finish earlier than they would with a standard dependency.
Can Be Used in All Relationships: Lead can be applied in Finish-to-Start (FS), Start-to-Start (SS), Finish-to-Finish (FF), and Start-to-Finish (SF) relationships.

Examples of Lead Time:

Example 1: Manufacturing Project (Finish-to-Start with Lead)

Predecessor Activity: Complete assembly of product components.
Successor Activity: Start testing the product.
Lead: -2 days.

In this case, the testing team can begin testing 2 days before the assembly is fully completed. The overlap (lead) ensures that the project moves faster by allowing testing to begin while the final parts of the product are still being assembled.

Example 2: Road Construction (Start-to-Start with Lead)

Predecessor Activity: Start grading the road.
Successor Activity: Start paving the road.
Lead: -3 days.

As soon as grading begins, the paving activity can start 3 days later, even if grading is not fully completed. This overlap helps accelerate the project by starting the paving early.

Lag and Lead in Different Relationships

Lag and lead can be applied to various types of activity relationships, allowing for more flexibility in how activities are scheduled.

Finish-to-Start (FS) with Lag or Lead:

Lag: The successor starts a certain time after the predecessor finishes.
Lead: The successor starts before the predecessor finishes, overlapping the end of the predecessor.

Start-to-Start (SS) with Lag or Lead:

Lag: The successor starts a certain time after the predecessor starts.
Lead: The successor starts before the predecessor starts, overlapping the start of the predecessor.

Finish-to-Finish (FF) with Lag or Lead:

Lag: The successor finishes a certain time after the predecessor finishes.
Lead: The successor finishes before the predecessor finishes, overlapping the completion of the predecessor.

Start-to-Finish (SF) with Lag or Lead:

Lag: The successor finishes a certain time after the predecessor starts.
Lead: The successor finishes before the predecessor starts, overlapping the start of the predecessor.

How to Apply Lag and Lead in Primavera P6

To apply lag or lead in Primavera P6:

Select the Relationship: Go to the Relationships tab for the activity.
Input Lag/Lead Value: Enter a positive value for lag or a negative value for lead.
Save Changes: Primavera P6 will automatically adjust the schedule based on the lag or lead entered.

Advantages of Lag and Lead

Lag:

Allows for proper sequencing: Ensures that time-sensitive tasks have adequate waiting periods (e.g., curing concrete, drying paint).
Prevents resource conflicts: By delaying successor activities, lag can help avoid resource overloading or scheduling conflicts.

Lead:

Accelerates the schedule: Lead time enables overlapping activities, helping to shorten the overall project duration.
Improves resource utilization: By overlapping tasks, lead can maximize the use of available resources, avoiding idle time.

Challenges and Considerations

Overuse of Lag or Lead: Applying too much lag or lead can create unnecessary complexity in the schedule, making it harder to track and manage dependencies.
Resource Availability: Introducing lead time can cause resource constraints if the necessary resources are not available to start the successor activity early.
Risk of Delays: Lead can introduce risk if one activity starts too early before the necessary work from the predecessor is complete, potentially leading to rework.

Conclusion

Lag and lead time are essential tools in Primavera P6 for fine-tuning activity schedules and managing dependencies between tasks. Lag introduces necessary delays to account for real-world conditions, while lead accelerates the schedule by allowing activities to overlap. Understanding when and how to apply these adjustments can help project managers optimize their schedules, ensuring more efficient project execution and better resource utilization.