Project managers who’ve been around the block know that even the best-laid plans can go awry. Instead of letting a delayed task derail the entire project and disrupt delivery, those PMs use float to manage delays and steer the project to on-time completion. But what is float in project management? And how can PMs use float alongside various project management frameworks?

What is project management float?

Put simply, project management float is the amount of time a given task can be delayed without causing a delay in the entire project. But, there’s a little more to it than that. In fact, there are two distinct types of float that project managers use to manage task timelines: total float and free float

Let's look at some of the distinctions between the two.

Total float

  • The total amount of time a task can be delayed without affecting the final project delivery date
  • Usually what PMs are referring to when they talk about "project float"
  • Can compromise a project's final delivery date and is of more concern than free float

Free float

  • The amount of time a task can be delayed without impacting other tasks in the path
  • Referred to less often than total float
  • Usually not a huge concern to project delivery

Benefits of float in project management

As you can imagine, project float — sometimes called project “slack” — is highly beneficial for project managers, particularly those who oversee large, complicated projects with multiple task paths. Of course, project float helps tremendously with resource management, scheduling, and keeping projects on track for a timely delivery. But float is also extremely valuable for PMs working with contractors and internal resource managers. 

For example, by knowing precisely how much free float and total float a particular task has, you give your contractors more leeway to work with. This means they can optimize their schedule by choosing the best crew for the job, working as materials arrive, working in the best weather conditions, and avoiding overtime. 

Similarly, internal resource managers benefit from the flexibility project slack provides. Instead of feeling pressured by tight, non-negotiable deadlines, project float gives them the breathing room needed to allocate resources in the most efficient manner possible. 

How to calculate float in project management

Before you can calculate total or free float, you must first identify and map your project’s critical and non-critical tasks. Of course, the tasks that make up your critical path are dependent on one another. By definition, then, there will be no float in the project’s critical path. However, in complex projects that contain more than one task path, float will come into play in your non-critical paths. 

With your critical and non-critical task paths identified and planned, it’s time to calculate your float. These can actually be calculated with a simple formula.

To calculate total float, subtract the task’s earliest finish (EF) date from its latest finish (LF) date. It looks like this: LF - EF = total float. Alternately, you can subtract the task’s earliest start (ES) date from its latest start (LS) date, like this: LS - ES = total float. Both of these formulas will give you the task’s total float. 

Free float, on the other hand, is calculated by subtracting the task’s earliest finish date from its earliest start date. That formula looks like this: ES - EF = free float. 

An example of float in project management

Let's look at a simple example of how float can arise in a project.

Imagine you are building an extension on the ground floor of your home, and you set a deadline of six months. In order to build the extension, the following tasks need to be completed:

  • Laying the foundations
  • Plumbing and electricity
  • Plastering and painting
  • Laying the floor

The plumbing and electricity cannot be installed until the foundations have been properly laid, which will take six weeks. However, in your project schedule, you have allocated eight weeks for foundations to be laid. This means that laying foundations can start two weeks after your project's start date without affecting the scheduled installation of plumbing and electricity. The float for laying the foundations is, therefore, two weeks. 

How to use float for better project management

No matter your preferred project management framework or style, understanding total and free float can help you and your teams improve resource management, internal and external scheduling, and project delivery. The great part about float is that it can be implemented in just about every PM framework, including Agile, Kanban, critical path, PERT, waterfall, and more. 

Of course, by leveraging a proven project management software platform like Wrike, you’ll have all the tools you need in one convenient place. Wrike’s interactive Gantt charts make it simple to see exactly where a project is at any given time while giving you insight into total and free float among your project’s tasks.

If you’d like to see exactly what Wrike can do for you and your project teams — and how float can help you get the most from your next project — start a free two-week trial today.