Lag

May 27, 2025
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What is Lag?

Lag in project management refers to the intentional delay between two tasks that are dependent on each other. The project manager schedules a successor activity to start a specified amount of time after its predecessor has finished. They commonly use this concept in network diagrams and the critical path method (CPM) scheduling. It helps project managers plan and sequence work realistically, often to account for constraints such as drying time, delivery schedules, or required approvals. Unlike delays caused by unforeseen issues, lag is planned and built into the project timeline to reflect real-world conditions.

Key Points

  • It represents a scheduled gap between tasks in a project plan.
  • Teams measure it in units of time, such as days or weeks.
  • It differs from delay, which is unplanned and typically undesirable.
  • It is most commonly used in finish-to-start task relationships, though it can apply to other dependency types.
  • Project scheduling tools, like Gantt charts or CPM diagrams, often display lag as a visible buffer between tasks.

Related Terms

  • Lead time is the opposite of lag and refers to overlapping tasks where the successor starts before the predecessor finishes.
  • A dependency is the relationship between two tasks, which determines the presence and duration of lag.
  • A critical path may include tasks with lag, but the overall project duration depends on whether the lag affects the total time of the sequence.
  • Project managers can delay a task for a certain amount of time, called float or slack, without affecting the project timeline, and they may adjust it when they introduce lag.
  • A schedule baseline includes all planned lags and is used to compare actual progress against the project plan.

Lag: Example

Consider a construction project where workers must pour concrete and then wait for it to cure before building walls on top of it. If concrete takes three days to cure, the wall-building task cannot begin until three days after the concrete is poured. This planned three-day gap is an example of lag. It ensures that dependent tasks follow logical, safe, and efficient timelines.

Lag: Best Practices

  • Identify and document all necessary lags during the project planning phase.
  • Use project management software to represent it clearly in the schedule.
  • Communicate it with stakeholders to manage expectations and reduce confusion.
  • Regularly review and adjust it as needed to align with changes in scope or external factors.
  • Avoid excessive lag, as it can create inefficiencies and unnecessarily extend the overall project duration.

Additional Resources

Lag - Project Planning, Scheduling, and Control, Sixth Edition: The Ultimate Hands-On Guide to Bringing Projects in On Time and On Budget     Lag - Project Management: A Systems Approach to Planning, Scheduling, and Controlling

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