Lead vs Lag
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Designed to help those that are preparing to take the PMP or CAPM Certification Exam, each post within this series presents a comparison of common concepts that appear on the PMP and CAPM exams.
Lead vs Lag
Lead and lag are two terms associated with the relationships that may occur between multiple schedule activities.
Lead
Lead is the acceleration of a successor activity. In other words, the second activity can begin (and be conducted in parallel) as the first activity.
Lead is only found activities with finish-to-start relationships: A must finish before B can start.
In order to leverage a lead, which will compress the total combined duration of both activities, the dependency must be discretionary, meaning that there is no physical limitation on completing A before B begins.
Lag
Lag is the delay of a successor activity and represents time that must pass before the second activity can begin. There are no resources associated with a lag.
Lag may be found in activities with all relationship types: finish-to-start, start-to-start, finish-to-finish, and start-to-finish.
Example
The photo shoot will take four days and the photo editing will take six days. Instead of waiting until the end of the 4-day photo shoot to begin editing the pictures, we start editing after the first day of shooting. This brings the total duration from ten days down to seven days by leveraging the lead.
The photo proofs are sent to the customer upon completion of the shoot, however, there is a 15-day lag associated with the customer review before the printing of the photos can begin.
Summary
Lead and lag are both used in the development of the project schedule.
Lead is an acceleration of the successor activity and can be used only on finish-to-start activity relationships.
Lag is a delay in the successor activity and can be found on all activity relationship types.
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Thanks, very helpful
Thanks so much for this explanation!!! Helped a lot.
I’m guessing that these terms are misused frequently. For example, when talking about a item that has been ordered, a lead time is often quoted. Shouldn’t it be lag time, as it delays a finish-start relationship rather than accelerating it? Or, perhaps since they may actually be manufacturing the item that you have ordered concurrently to your project that makes it a lead? It’s still delaying the finish start sequence though…. I’d appreciate clarity on my confusion.
Hi Scott,
Yes, you are definitely correct! There is some confusion on the application of the terms within the general population as compared to specifically as it relates to activity dependencies. From a project management perspective, any type of delay between two dependent activities would be considered a lag. Lags can be found in any type of activity relationships (FS, SS, FF, SF) Lead is the overlap of two sequential activities that have a FS discretionary relationship, allowing the team to save time by the acceleration.
One great way to remember lead is to think of baseball and “leading off” the base.
In general context, the term “lead time” is used to convey time needed before delivery. So definitely a different context than the project management terms! Hope that helps!
OMG these videos are so helpful. You are very concise with your explanations and the videos are the perfect length. Very grateful to have found these as I prepare for my PMP. Thanks!
Excellent