What is Float in Project Management & How to Calculate It

Managing projects involves balancing many tasks and deadlines. Even a minor disruption, like team members getting sick, can jeopardize the entire timeline. 

Such uncertainties put a lot of pressure on project managers who must keep projects on track despite setbacks. 

The good news is that understanding project management float can help you avoid significant project delays.

Knowing how much float you have will give projects flexibility to absorb delays without affecting the final deadline. 

In this article, you’ll learn how to calculate float for better planning and deadline management. 

Let’s dive in. 

What is float in project management?

In project management, float is how long a schedule can be delayed without impacting the final deadline.

By calculating the amount of float each task has, a project manager will know what deliverables can be delayed and how much flexibility they have. Ultimately, this leads to better planning and keeping the project’s schedule on track.

In project management, there are many types of floats, including total, free, and zero floats, which we will discuss in more detail below.

Benefits of float in project management

Float can help teams, projects, and businesses deliver projects on time, but only when accurately calculated. 

The main  benefits of float are all about project flexibility:

• Buffer for delays: Float adds a buffer to keep the overall project timeline intact, when individual tasks get delayed. 
• Risk management: It gives project managers valuable information on managing risks and planning for possible project issues. 
• Rebalance workloads: When everybody has the right amount of work, stress is easier to manage, and tasks are more likely to be finished on time. 
• Accommodate last-minute changes: It also adds some wiggle room to a project’s timeline. Project managers can use float to prioritize time-sensitive tasks, like edits, and accommodate schedule changes. 

What are the different types of float?

Float in project management comes in various forms, each adding a level of flexibility to a project’s schedule.

Here are the seven most popular types of float: 

• Total float: It calculates how long a task can be delayed without impacting the project’s final deadline.
• Free float: The amount of time a task can be delayed without affecting the start date of any dependent tasks.
• Project float: The allowable delay time of a project before it affects clients or customers. 
• Interfering float: The float time of non-critical tasks that don’t impact the project’s outcome as much as critical tasks.  
• Independent float: The maximum delay time of critical tasks without impacting their dependent tasks and the project timeline. 
• Negative float: The time a project must recover when tasks extend beyond their initial deadline. 
• Zero float: When a task has no spare time and must start and finish exactly as scheduled. 

Before we talk about how to calculate each float type, let’s look at why this is different from slack time 👇  

How does float differ from slack time?

Float and slack time are used interchangeably in project management. 

Both refer to the amount of time you can delay tasks without impacting the next deliverables or the entire project. 

The difference is the context:

• Project slack is the common term for projects that use agile methodologies or work breakdown structures. 
• Float is used for other techniques like the critical path method (CPM). 

It’s a small (but important) difference to remember as we dive deeper into float.

How to calculate project float?

Here’s how to calculate float in project management in five steps:

Let’s take a look at each step in detail.

Step 1: Draw a task network diagram

The critical path consists of dependent tasks directly impacting the project’s final deadline. Tasks on the critical path have zero float, which means any delay in these tasks will directly delay the whole project. 

Here’s an example of identifying the critical path for a website development project. 

List all project activities, durations, task dependencies, and constraints. 

For example, let’s imagine a simple project with the following tasks:

Task	Duration (t)	Depends on
A	3
B	4	A
C	2	A
D	3	B, C

It’s task network diagram is as below.

In the network diagram, each node represents a task and its duration (t). The arrows represent the dependencies between the tasks.

Step 2: Find the earliest start (ES) and earliest finish (EF) for each task

For our example project, these calculations are as below:

Task	Duration (t)	Depends on	Earliest Start	Earliest Finish
A	3		0	3
B	4	A	3	7
C	2	A	3	5
D	3	B, C	7	10

On the network diagram, the ES and EF are shown below:

Step 3: Identify the critical path

The path with the longest duration through these connected tasks is the critical path.  

For our example project, the longest path is highlighted in red below:

This path shows the minimum duration needed to complete the project. In our example project, this duration is ten days.

Step 4: Calculate the late start (LS) and late finish (LF) for each task

LS is the last possible date you can begin a task before it impacts the project’s final deadline. The LF is the latest possible date to finish a task without affecting the critical path.  

We work backwards from the project’s end to calculate the LS and LF.

For our example project, the calculations are shown in the network diagram below:

Or as below in table format:

Task	Duration (t)	Previous node	Latest Finish (LF)	Latest Start (LS)
D	3		10	7
C	2	D	7	5
B	4	D	7	3
A	3	B, C	3*	0

*Choose the LS of Task B as Task B is on the critical path.

Step 5: Calculate the total float of the task

Total float (or simply float) of a task is the amount of time a task can be delayed without delaying the entire project’s completion date.

Float (F) is calculated using the following formula:

For our example project, the calculations are:

Task	Latest Finish (LS)	Earliest Start (ES)	Float (F)
A	0	0	0
B	3	3	0
C	5	3	2
D	7	7	0

Tasks A, B, and D have zero float, meaning any delay in these tasks will delay the entire project. 

Task C has a float of 2 days, which means it can be delayed by up to 2 days without affecting the project’s completion date.

Alternatively, you can calculate the float by finding the difference between the latest finish (LF) and Earliest finish (EF) for each task.

For our example project, the calculations are:

Task	Latest Finish (LF)	Earliest Finish (EF)	Float (F)
A	3	3	0
B	7	7	0
C	7	5	2
D	10	10	0

Step 6: Calculate other float types (if needed)

Depending on how complex a project is, you might need to calculate and use other types of floats: 

• Free float: Free float is the amount of time a task can be delayed without delaying the start of any subsequent tasks.

• Interfering float: Interfering float, also known as interfering slack, is the amount of time a task can be delayed without delaying the project’s completion date but may delay the start of some subsequent non-critical tasks. It is the difference between total float and free float.

• Independent float: Independent float, also known as independent slack, is the amount of time a task can be delayed without affecting the start of any subsequent tasks or the project’s critical path.

• Total project float: Total project float is defined as the amount of time a project can be delayed without delaying the project completion date. Since the critical path sets this final deadline, any delay in tasks on the critical path will directly delay the project’s completion. So, generally, the total project float is zero.

Best practices for managing float

Calculating and managing float are two different things.

Here are some best practices for managing project float: 

1. Categorize tasks as critical or non-critical

Knowing which tasks are critical empowers project managers to schedule and prioritize work more efficiently. 

If you can separate critical and non-critical paths to better focus efforts, your team can spend time on tasks with zero or little float time.

The result is better project planning, fewer delays, and more projects delivered on time 👌

2. Pay attention to resource allocation

Project managers must ensure critical tasks are well-supported with the right resources when using float.

With resource management software like Toggl Plan, it’s clear who’s working on what and when.

The Team Timeline feature shows many things that help project managers allocate resources more effectively:

• Who is responsible for completing the task
• What project is the task part of
• The status of each task
• Task notes or checklists

To access the Team timeline, you must first create a new team:

• Click the ‘+’ sign on the sidebar next to the Teams section.

You can access the Availability Overview feature on any Team Timeline, which shows each team member’s available hours. 

To open the Availability Overview panel, click on Show Availability, as shown below.

3. Open the lines for continuous communication

We all want to run projects smoothly and avoid roadblocks. But things go wrong, delays happen, and projects go off track. At this point, communication is often the difference between success and failure. 

Keeping everyone on the same page makes it easier for them to understand the project timelines, task status, and any changes that may affect deadlines. 

Even if issues arise, communicating effectively makes it more manageable to handle project changes. 

What are the limitations of using float?

Float isn’t a magic bullet for project scheduling, and like any project management technique—it has limitations. 

Here are some things to remember when using float, especially when managing complex projects:

• Float assumes workflows are linear and predictable. However, complex projects with interdependencies and unforeseen delays rarely work this way. 
• Deciding which paths are critical and how to allocate resources can be difficult.
• Traditional float management may not be flexible enough for the necessary changes in complex projects. 

While float is a useful tool, it should be used alongside other project management strategies, such as risk management and resource leveling, to schedule complex projects. 

What mistakes should project managers avoid when using float?

To maximize the benefits of float, project managers should avoid:

• Overlooking task interdependencies: Always be mindful of how closely tasks interconnect. Misjudging these relationships can cause scheduling issues, quickly deplete available float, and delay projects. 
• Overreliance on float: Relying too heavily on float can give project managers a false sense of security and blind them to project risks. 
• Poor prioritization: Project managers who don’t set clear task priorities risk allocating float ineffectively.  

Understanding the downfalls of using float helps project managers use it wisely to keep projects on track. 

The bottom line

When used correctly, float helps project managers prevent delays and ensure projects are completed on time and within budget.

To enhance your project planning even more, you can try Toggl Plan for free and use it to:

• Easily create project timelines and manage project tasks
• Get a clear view of available project resources

Sign up for a free Toggl Plan account. 

Related articles:

• 10 Proven Project Management Tips For Small-Team Project Managers
• 10 Common Project Management Challenges And Their Solutions
• What is Project Resource Management? [Comprehensive Guide]