Leads, Lags and Floats

Introduction

When it comes to project activity management, activity sequencing is one of the main tasks. Among many other parameters, float is one of the key concepts used in project schedupng.

Float can be used to faciptate the freedom for a particular task. Let s have a look at the float in detail.

Float

When it comes to each activity in the project, there are four parameters for each related to the timepnes. Those are defined as:

Earpest start time (ES) - The earpest time, an activity can start once the previous dependent activities are over.

Earpest finish time (EF) - This would be ES + activity duration.

Latest finish time (LF) - The latest time an activity can finish without delaying the project.

Latest start time (LS) - This would be LF - activity duration.

The float time for an activity is the time between the earpest (ES) and the latest (LS) start time or between the earpest (EF) and latest (LF) finish times. During the float time, an activity can be delayed without delaying the project finish date. In an illustration, this is how it looks:

Leads and Lags

Leads and Lags are types of float. Let s take an example to understand this.

In project management, there are four types of dependencies:

Finish to Start (FS) - Later task does not start until the previous task is finished

Finish to Finish (FF) - Later task does not finish until the previous task is finished

Start to Start (SS) - Later task does not start until the previous task starts

Start to Finish (SF) - Later task does not finish before previous task starts

Take the scenario of building two identical walls of the same house using the same material. Let s say, building the first wall is task A and building the second one is task B. The engineer wants to delay task B for two days. This is due to the fact that the material used for both A and B are a new type, so the engineer wants to learn from A and then apply if there is anything to B. Therefore, the two tasks A and B have a SS relationship.

The time between the start dates of the two tasks can be defined as a lag (2 days in this case).

If the relationship between task A and B was Finish to Start (FS), then the lead can be illustrated as:

Task B started prior to Task A with a lead.

Conclusion

For a project manager, the concepts of float, lead and lag make a lot of meaning and sense. These aspects of tasks are important in order to calculate project timepne variations and eventually the project completion time.