What is Float, and How Can It Help Maintain Your Project Schedule?

project management float

Float and slack in project management


To the uninitiated, downtime in the middle of the project is assumed to be unequivocally bad. Surely, if your team is downing tools or has nothing on the agenda for a couple of days, the project isn’t being managed correctly. Either that or the team is slacking off, right?

Think again. In an ideal world, tasks would run seamlessly back to back, carrying the project from conception to completion in one smooth movement. However, downtime is a given in any project. Sometimes it’s planned for, such as when project teams are awaiting feedback, and other times it’s unplanned. Unfortunately, no matter how many times you go over your plans to ensure they’re water-tight, tasks will be delayed. In the case of unplanned downtime, great project managers prevent their projects from being derailed by mitigating issues by understanding float.

What is float in project management?

When discussing project management, we’re generally talking about large projects that are made up of a significant number of smaller tasks. These tasks tend to depend on one another, which means that if one is delayed, it can impact the entire project. The worst-case scenario is that it delays delivery.

That is where float, also known as slack, comes into play. Float is a numerical value representing the maximum amount of time a task can be delayed before it causes a domino effect, delaying the start of other tasks. This is often used alongside the critical path method, which helps project managers schedule activities effectively and calculate how long it will take to complete a project.

In order to use float correctly, project managers need to understand the difference between the two types of float: total float and free float.

Total float vs. free float

When project managers mention ‘float,’ they’re typically referring to ‘total float’. However, both types are critical to project management.

  • Total float: The amount of time a task can be delayed before it begins to impact the delivery of the entire project.
  • Free float: The amount of time a task can be delayed before it delays subsequent dependent tasks.

The reason total float comes up in conversation more often is because it dictates the level of flexibility within the project as a whole, and going over a task’s total float can have a significant impact on the final delivery of a project. Free float, on the other hand, is useful at the task level; a delay to one task with free float won’t impact the entire project.

How can float in project management be calculated?

Let’s look at how float is calculated and the role it plays in the critical path method.

While project managers will likely never need to calculate float manually — that’s what project management tools like Forecast are there for — it bears understanding how it works.

Understanding your tasks and critical paths

The first step is to understand which tasks are critical to your project hitting its delivery date. One way to do this is to visually map out your tasks in order of completion by creating a network diagram. This will help you see task dependencies, which is crucial to determining float. 

Using this process, you begin by adding each task’s earliest start. The start date of subsequent tasks will be determined by the duration of its predecessor. For example, if the first task’s earliest start is assigned a value of zero and has a minimum duration of 5 days that means its earliest finish will have a value of 5. Any subsequent tasks’ earliest starts will also have a value of 5.

You should also map out each task’s latest start and finish. If the first task could possibly be pushed back a day, that would mean its latest start would have a value of 1 and its latest finish, a value of 6.

Some tasks will have no flexibility in their start date. That means they have no float. If multiple tasks run together in this way, with the completion of one task triggering the start of the next with no room for delay, this is known as a critical path.

Identifying critical paths

Project managers use the critical path method to calculate how long a project will take to complete. Understanding the critical path helps teams uncover the longest sequence of tasks that must be completed as well as the total effort required to complete the project. That helps project managers plan their resources and manage stakeholders.

Calculating float

It’s important to remember that free float can never be more than total float; it must always be equal to or less than total float. 

    • Total float: To calculate the total float of a task, subtract the task’s earliest finish from its latest finish. This provides the maximum number of days a task can be delayed without impacting the project’s planned end date. The latest finish marks a boundary that cannot be surpassed without delaying the entire project. If a task’s total float is delayed by even one day, the entire project will be delayed. You can also complete the calculation by subtracting the earliest start from the latest start.
  • Free float: To calculate the free float of any given task, simply determine the difference between this task’s earliest end date and the next task’s earliest start. If multiple tasks are dependent on the completion of the current task, use the start date that will occur first.

Make a note of these simple calculations:

Total float = LF - EF or LS - ES

Free float = ES of the first subsequent task - EF of the current task

Example calculations of slack in project management

In this example of slack in project management, your team is building a website for a client. After accepting the brief, you have three months to complete the project. There are multiple critical tasks, including:

  • Research
  • Content creation
  • Wireframing and design
  • Coding
  • QA

Each of these tasks can be broken down into smaller tasks, but we’ll remain at the top level for the sake of simplicity. While some tasks can be completed concurrently, making them non-critical, most of these larger tasks can’t be started until the preceding task is complete.

Let’s say you’ve allocated three weeks for content creation and four weeks for wireframing and design. In your plan, both these tasks can be worked on simultaneously and are dependent on the completion of the research phase, which is planned to take two weeks. 

That sets the earliest start date for both of these at after two weeks. However, both tasks have the same dependent task, coding, which has the earliest start date of six weeks after the commencement of the project and no total float. That means the content phase has a float of one week; it can be delayed by up to one week before it begins impacting the start of the coding task and therefore pushing the project’s end date back. The wireframing and design phase, however, has a zero float and forms part of a critical path.

What are the benefits of float in project management?

Float can feel extremely technical at first, but it is a relatively simple and effective way to help teams understand the importance of sticking to a schedule. 

Monitoring progress

Getting a project over the line on or before its planned delivery date is top of any project manager’s priority list. Monitoring float is a critical part of ensuring delivery. Total float provides clear evidence of when a project has little to no margin for error, allowing project managers to make calls about bringing in additional resources or providing motivation if their team is running behind.

If delays occur early on, that will reduce the total float for the remainder of the project and put pressure on managers to prevent further delays. If a project’s float is nearing zero, project managers know it’s time to begin managing stakeholders’ expectations.

Optimizing productivity

People don’t like being worked to the bone, understandably. Project managers that keep an eye on a project’s float will know early on when they’ll need to bring in additional resources to support their team rather than pushing people to work harder to meet tough deadlines.

Likewise, it can be helpful to show unmotivated teams the importance of maximizing efficiency to ensure deadlines are met.

How to manage float with project management tools

Now that you understand how float works, it’s time to hand over the stress of managing calculations to your project management tools.

Gantt charts

Gantt charts are particularly helpful at providing a visual breakdown of your project schedule, including task durations and dependencies. They’re particularly useful for waterfall projects, and can quickly calculate how delaying a task will impact the long-term success of the project.

Project dashboards

Automated project dashboards are linked to your team’s output; every time they mark a task as completed, it’ll update the project’s progress. This is especially helpful for project managers to see progress in real-time and understand what tasks are at risk of being delayed.

How Forecast can help you track your progress effectively

Forecast takes the stress of calculating float off your hands. After all, you have more pressing matters to deal with than subtracting EF from LF.

Our Advanced Analytics (AvA) platform gives you all the tools you need to understand your project’s progress at a glance and more. With real-time insights that reflect your team’s output, you can make critical decisions in seconds, reducing the impact of delays or mistakes on your delivery. Plus, Forecast automatically notifies you when a task is behind schedule, so you can focus on delivering top-quality work.

Try Forecast out for yourself by signing up for a free trial below.

Subscribe to the Forecast Newsletter

Get a monthly roundup of productivity tips & hacks delivered straight to your inbox