Lead and Lag
Not all project tasks start as soon as the preceding tasks finishes. Sometimes there is a delay, or an overlap between the tasks. This is called ‘Lead’ or ‘Lag’. When creating the project dependency chart it is important to consider if there is any ‘Lead or Lag’ time. Always link tasks at the lowest level – and never link work-package or summary tasks.
The overlap between two tasks is called ‘Lead’ time. It happens when you can start the second task before the first task is completely finished.
To enter ‘Lead’ into Microsoft Project you need to enter a negative ‘Lag’ number. As an example, -2 days of ‘Lag’ is the same as 2 days ‘Lead’.
A delay between two tasks is called ‘Lag’ Time.
In common use we often say that “The parts need to be ordered now because they are on 20 days lead time”. However, this is actually a description of a delay or ‘Lag’ time.
One problem with ‘Lag’ time is that it is not clearly explained, and shows as a gap between tasks. I recommend that you add a dummy task to be explicit about what the delay is for. There will be no resources or costs assigned to the dummy task, but it will clearly explain why there is a delay.
Examples of Lead and Lag
Here are some examples:
- Lead Time Examples:
- Painting a large room, the second coat can be applied to the first wall before the first coat is applied to the last wall
- Laying a pipe, the previous section can be back-filled whilst the next section has the trench dug
- Manufacturing 5 castings, the first one can be machined as the fourth one is cast
- Lag Time Examples:
- Transport of goods between two sites
- Waiting for Paint/Cement to dry or any other chemical process
- ‘Heat-Sink’ for 24 hours of electrical equipment
‘Lead’ time can save time on a project, especially if the tasks are on the critical path.
This short 3 minute video explains the concept.
The following 3 minute video shows how to add Lead and Lag in MS Project
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Lead and Lag can be applied to all different relationship types, Start-Start, Start-Finish, Finish-Finish as well as Finish-Start.