Even the most carefully planned project can experience delays. Luckily, project managers know that they can use float or slack to get their project back on track. Sounds great! But what exactly is float in project management? And how can you use it to benefit your schedule?


What is Schedule Float in Project Management?

In project management, “float,” or “slack,” is the amount of time that a task can be delayed without delaying the next task or the entire project. Think of float as the safety net between tasks that gives you a little leeway for error. As you might have guessed, float can be extremely beneficial in project management. But, before you can utilize it, you’ll need to know what type of float you’re dealing with, and how to calculate it. 

Types of Float


There are two main types of float:


  • Total float – total float is the amount of time you can delay a task before it impacts the final result of the project


  • Free float – free float is the amount of time you can delay a task before it impacts the next task in the schedule


* Total float is going to be the float you’ll be most concerned with as it immediately affects the overall project. Still, free float is worth considering. 

What is CPM?

Float is an essential element of the “Critical Path Method,” commonly written as CPM. In project management, you can use the CPM to determine the duration of a project through a sequence of tasks. You must complete tasks along “the critical path” in a specific order to complete your project within your established timeline. 


* The critical path is the longest sequence of tasks that must be completed in order to finish a project. By adding up the duration of all tasks along the Critical Path, you can calculate how long it will take to complete the total project.


Tasks that are on the critical path have a float of zero – meaning they have no slack and MUST be completed in order to finish the project. Other tasks exist on the timeline but aren’t considered to be on the critical path – these tasks typically have positive float. This means that they have slack and you can move or delay them without definitely impacting other tasks or the overall project. 


*The less float a task has, the less flexibility it has.


*a task with zero float MUST be completed in their original time allotment in order to complete the project on time. 

Examples of Float

Now that you have a basic understanding of float, let’s look at a simplified example of float on a schedule. Imagine that you are remodeling a bathroom for a client who needs the project done in a certain number of weeks. Here are the tasks you must complete:


  1. Drywall Installation
  2. Plumbing and electrical
  3. Plastering the walls
  4. Tiling the floor
  5. Painting
  6. Decoration


In the CPM, tasks 1 – 4 would be considered part of “the critical path,” meaning they have zero float. You MUST complete these tasks on time – and in order – to complete the project on time. However, tasks 5 and 6 have more flexibility. You could paint the walls either before or after tiling the floor. Likewise, you could decorate the bathroom with accents like knobs and hooks before or after painting. Essentially, in this basic example, painting and decorating are the tasks that have float- thus they are not adhered to the critical path and can be moved and adjusted to benefit the schedule. 


The Importance of Float in Project Management

As you may have guessed, float can be extremely beneficial in project management. Not only can you use float to edit your schedule, assign tasks, and manage resources, you can also use it when working with hired contractors and other professionals. That’s because when contractors know the float available in the project they can prepare their own crew, schedules, and equipment arrival times in the best way possible to avoid delays. Other professionals both inside and out of your organization will find float extremely useful because they won’t feel pressured by a timeline with completely non-negotiable deadlines. With float, they’ll have the cushion to reallocate tasks and resources to make the project as efficient as possible. 

How to Calculate Float 

Now you’re probably wondering how you can accurately calculate float to get the most out of your project schedule. Truthfully, calculating float – especially on large and ever-changing projects- can get complicated. Luckily project management software like Primavera P6 and Oracle Primavera Cloud can quickly and automatically calculate float in real time. 


*Some popular project management software that automatically calculates float are Primavera P6 and Oracle Primavera Cloud. At Taradigm, we get you set up with these programs. Plus, we offer Primavera P6 and Oracle Primavera Cloud training courses taught by our experienced, professional trainers. 


Calculating Float Manually

Of course, if you’re mathematically curious, you can still try to calculate your float manually. In order to do so you must identify the critical and non-critical tasks on your project’s timeline. 


Next,  you’ll first have to calculate the following values for each task that you wish to calculate float for:

  • Duration (Dur) — the estimated duration of the task 
  • Early start (ES) — the earliest point you can start an activity
  • Early finish (EF) — the earliest point that you can finish a task
  • Late finish (LF) — the latest point that you can finish a task without affecting the project’s deadline
  • Late start (LS) — the latest point at which you can start a task without affecting the project deadline

Once you have figured those out, you can use this simple formula to calculate your float:


Total Float Formula:


To calculate the total float of a task, subtract the latest finish date/time (LF) from the earliest finish date/time. You can also subtract the latest start time (LS) from the earliest start date/time to get your task’s total float. 


Total Float = LF – EF OR   Total Float = LS – ES


 *Remember: Total float is the amount of time a task can be delayed before it impacts the final result of the project


Free Float Formula:


To calculate free float, use the same formula as above! The only difference between total and free float is that one belongs on the critical path and the other does not. Essentially, the two types of float have the same formula because their only difference is the context in which you use them. 

Free Float = LF – EF OR   Free Float = LS – ES


Negative Float

Another type of float we should mention that you may run into is negative float. Negative float is essentially a delay in the project. While tasks on the critical path cannot have positive float, sometimes they can acquire negative float. Negative float can cause a delay to the next activity or the overall completion of the project. For example, an activity with -2 days of float will need to be completed 2 days earlier than its finish date for the activity to finish on time. If an activity has negative float, you will want to resolve it to ensure your project is able to be completed on time. For detailed information on negative float and how to calculate and resolve it in Primavera P6, see this article

How Float and Float Calculations can Help Your Project 


  • Keeps your project on track- Knowing what float your project has available- or lack thereof- can keep your project on track. If the overall project’s float or even a given task’s float is getting close to zero, you’ll know you need to focus to get the job done on time. 

  • Prioritize tasks-  Knowing each task’s float gives you the power to prioritize tasks. For example, if a given task has a lot of float, you can focus on other tasks that have lower float in order to get the project done as efficiently as possible. 

Boost confidence- You’ll find that with transparent float, you and your team will gain more confidence in completing tasks. When you have the ability to foresee delays or slack, everyone is more at ease.


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