Float is a project management concept that is used more often than it’s thought about.

In other words, as a project manager, you’ll likely use one of the two types of float — free float or total float — without really realizing that’s what you’re doing.

Let’s take a quick look at float and its uses in project management.

What is Float in Project Management?

Float, also referred to as Slack, is the amount of time an activity can be delayed before it affects something else.

Pretty simple concept.

In practical terms, how long can we wait to begin — or finish — task A, before it begins to affect our ability to start on — or complete — task B?

That duration for task A is float.

But which type of float are we talking about in that scenario?

Difference Between Free Float and Total Float

There are two key types of Float: Free Float and Total Float.

Typically, when you see references to just “float,” as you did in the above section, that concerns Total Float.

One way to distinguish the two terms is by keying on the word “total,” which can serve as a reminder that we’re talking about a potential impact on the total project.

Free Float in Project Management

Free float refers to the amount of time any activity can be delayed before it affects the early start of any successor activities.

So if activities B and C cannot be started until activity A is finished, the amount of time available to finish activity A without running into the early start times for activities B and C is the Free Float.

Total Float in Project Management

Total float refers to the amount of time any scheduled activity can be delayed, from its early start time, before it will have an impact on the entire project schedule.

So while free float is concerned specifically with how a single activity’s timeline will affect the activities that must follow it, total float looks at how that activity’s duration will affect the entire project’s timeline.

Why You Should Care About Float in Project Management

The concepts of free float and total float are frequently used in real-life project management, though not specifically thought of as such.

While creating project timelines, setting up Gantt Charts and other schedule-related documents, you’ll consider float without thinking about float.

Float will come into play when you’re estimating task durations, when you’re estimating the entire project timeline, when you’re running risk assessments and setting up contingencies, and when you’re problem-solving issues — such as delays — that inevitably arise during the course of a project.

You won’t necessarily say “OK, time to think about float!”

You’ll just simply do it, without typically thinking about float at all.

However, one place you do need to think about float, and make sure you understand the differences between its two types, is during preparation for the PMP Exam.

If you plan to get your Project Management Professional certification from PMI, plan to get familiar with free float and total float first.