There’s a key difference between lead time and lag time in project management that’s easy to forget. While both terms apply to recurring activities, each has its uses in a schedule analysis. Hence, the project manager uses both lead and lag metrics when assessing any project phase.

In essence, such reports show the actual work done on the site. It’s a way of weighing the efficacy of the project planning phase and whether the team follows the critical path.

What Does Lead Time Mean for Project Managers

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Complex projects comprise several steps; one segment must finish to start the next two or more tasks. Hence, the term lead time refers to the period needed for a one-time project or a crucial step. As a whole, it shows how fast the team was with the project schedule.

Therefore, the project management team envisions the lead time beforehand. Of course, if the goal changes mid-work, that projection will need an update. If done right, the lead time can serve as insurance for the completion of the work package.

When following the critical path method, the lead time can track each task’s progress from start to finish. Conversely, lead time also applies to tasks that have overlapping starting times. For example, if the follow-up task (the successor activity) begins before the previous one ends. Yet, most steps will have a start-to-start dependency.

As a result, lead time is not always a usable factor. Still, even when it has a negative value, it can be useful for project schedule management. Also, managers often use the lead time with schedule compression techniques like fast-tracking.

What Does Lag Time Mean for Project Management

On the other hand, lag time refers to the downtime between two tasks due to accidents. For instance, when one task depends on the completion of the predecessor activity. If there are issues with the prior task, there’ll be a lag time for the successor activity.

Other than that, this metric also refers to any delays between the tasks. The reasons for this can be diverse. But, if the team can foresee them, they can calculate those lag times in the timetable.

Usually, such lag times last for one or two days in a finish-to-start relationship. The team should be aware of this beforehand to ensure no other tasks suffer during that time. So, the project manager should set that lag time as a positive value.

Naturally, there can be many types of lag time in project management. They can even play the part of a safety net. Yet, the schedule network diagram should highlight them either way. In that way, the project team can oversee the chain of events better.

If the project planning phase fails to underline all lag times, it can lead to delivery delays. Then, if such problems keep on repeating, they can result in severe budget issues.

Lead Time vs. Lag Time in Project Management

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  • The lead time metric shows the time saved between activities. On the contrary – lag time refers to the waiting period before the work resumes. Hence, there’s a list of the usual lag indicators.
  • Lead times measure the time required for a single task or the whole project to finish. Lag time is the value of how much dependent tasks affect each other. In an activity sequencing process, both metrics are important.
  • In some cases, the lead time is merely the planned route, while the lag time is the result. This is mostly the case when an accident halts the progress.
  • In practice, managers use the “-” to mark lead times (i.e., FS-3). Since lag is idle time, the diagram shows it as a “+,” i.e., FS+3.
  • For two tasks to create a lead time, they should overlap at a certain point. If there’s downtime, it becomes a lag time.

How Managers Deal With Lag Time in Project Management

When crafting the network diagram, project managers shortlist the obvious lag indicators. That way, they build an idea for the overall project lag time. There are two routes for this task: the Arrow Diagramming Method (ADM) and Precedence Diagramming Method (PDM).

What sets them apart is their compatibility. So, the PDM method can use four types of dependencies. The list includes the start-to-finish, start-to-start, finish-to-start, and finish-to-finish types.

For the lead time metrics, only the finish-to-start working tasks are the focus. They occur when the next task cannot commence before the predecessor activity ends. In such cases, any lag time affects both of the tasks in the sequence.

Therefore, a project can have several types of both lead and lag times. For example, the follow-up task will begin while the first one is still ongoing. Similarly, an accident will happen that produces a two-day lag time before the successor activity.

Then, project managers will denote any and all such instances. If they need to make up for a period of time due to lag, they’ll put a positive value. Otherwise, any time savings produce a negative number in the network diagram.

Lag Time in Project Management – The Common Lag Indicators

To evaluate performance at the end of the project, managers inspect every step of the way. Also, they use real-world examples as reference points. Then, they review each of the key activity dependencies. Such an approach allows them to identify the total duration of the effective workflow.

Another byproduct is the ability to consider any lag indicator in time. So, if a project has a few recurring tasks, the team can recognize certain patterns. In that way, they can set new goals and keep on improving.

Lead and Lag Time in Project Management – Practical Appliances

Knowing which mishaps can cause a slowdown serves to soften the blow. In other words, it creates the space necessary to find a workaround. If possible, you can assign an early start to the second activity and free up some room for errors.

In practice, tasks often take three to four days to complete. So, that makes a total of seven days for two tasks. However, the second activity often follows a two-day lag time. Thus, the result is a total working time of nine days.

With that in mind, the manager can schedule the successor task to start two days before the end date of the first leg of the project. By making that change, the total period will amount to only seven working days. Granted, there might be resource constraints preventing this option.

If all goes smoothly, the project leads will denote the time saved as a “-” sign. For this example, the total duration will read 9-2=7.

How to Properly Utilize the Lead and Lag Times

This important concept focuses on the task of ironing out the common road bumps within a project. After using the PDM method, the team will spot the logical relationships they can later use. Hence, they can make them more or less flexible with leads and lags.

At the same time, this allows them to make the right changes mid-work. Various optimization strategies (like the critical path method) encourage that approach. For example, fast-tracking is one of the most effective time-saving techniques.

Conclusion on Lag Time in Project Management

Both lead and lag time play a deciding role when scheduling a project. However, leads appear only when assessing finish-to-start dependencies. Then, they are useful for figuring out how to further capitalize on such savings.

Lags are common for any kind of work dependency. In short, it’s any idle time when work cannot resume before the resolution of an issue. Hence, any network diagram clearly underlines the tag time so that the whole team can take note.

In that way, lead and lag time are among the essential tools for making a schedule baseline. By using them, the project lead can avoid obstacles and ensure a successful outcome.

If you liked this article talking about lag time in project management, you should check out this one with innovation frameworks.

I also wrote about similar topics like the benefits of project management, what is crashing in project management, project management forecasting, the s-curve in project management, what is a war room, and primary and secondary stakeholders.

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