Leads and lags are two important concepts when it comes to schedule management. These concepts are very easy yet play a very important role in the project schedule diagram or network diagram.
In this blog post, we will explain both terms with simple real-world examples and share the practical use of these concepts.
Why is this Important?
In an ideal world, all the project activities are sequentially lined one after the other. Let assume your project has 5 activities and all of them are sequentially lined one after the other. So as a project manager, it’s your responsibility to make sure all those 5 activities start and end based on your project schedule. But in some case, the Project Manager needs to intentionally speed up or delay the dependent activities while keeping the relationship at it is.
According to the PMBOK Guide 6th Edition, “A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor activity.”
In simple words, lead allows successor activity to start early. For Example, let assume that the time duration for the designing activity is 10 days and the time duration for the coding activity is 20 days. The designing activity is on its 5th day and you have started the coding activity. While there are still 5 days left at the end designing activity and the coding activity has started 5 days in advance before the design activity finishes. Here, the lead time will be of 5 days. The Project manager usually uses this technique to reduce the overall time of the project.
According to the PMBOK Guide 6th edition, “A lag is the amount of time a successor activity will be delayed with respect to a predecessor activity.”
It is opposite to lead, lag makes successor activity delay its start. For example, let assume that the duration of the developing activity is 20 days and the duration of the testing activity is 5 days. After completing the developing activity, you wait for 2 days, and then you start the testing activity. Here, the delay of 2 days is lag time.
Mathematical Representation of Leads and Lags.
Lag describes delay and it means the addition of time. The lag time is denoted by the plus sign (+) in the network diagram.
Lead describes advancement, this means a reduction in time. The lead time is denoted by the minus sign (-) in the network activity diagram.