Free Float vs Total Float

What’s the difference between a minor delay—and a major disaster? When your schedule’s on the line and every task feels critical, understanding free float vs total float can mean the difference between staying on track and falling behind. Yet despite their importance, these two terms are often confused, misused, or misunderstood entirely.

In project management, float refers to how much flexibility you have before a delay starts causing problems. There are three types—free float, total float, and project float—but the real PMP® exam focus is on free float vs total float. Whether you’re prepping for the exam or managing real-world projects, knowing when and how each float applies is essential for smart scheduling and keeping control of your timeline.

Know Your Float

In project management, float—also known as slack—refers to the number of days a task can be delayed without impacting the next activity or the project’s overall completion date. It’s a key concept tied to schedule development, network diagrams, and the critical path. Each type of float has its own formula, and anyone pursuing the PMP® certification must understand how these calculations support effective project scheduling and decision-making.

Total Float Formula:

Total float—also known as total slack—is the number of days an activity can be delayed without delaying the project’s final completion date. It’s one of the most important indicators of flexibility in your project schedule.

To calculate total float, you’ll use values that come directly from your network diagram, including:

• Early Start (ES) – the earliest an activity can begin
• Late Start (LS) – the latest an activity can begin without delaying the project
• Early Finish (EF) – the earliest an activity can finish
• Late Finish (LF) – the latest an activity can finish without causing delay

Here’s what you should keep in mind about total float:

• Each activity has its own total float value.
• Total float is always greater than or equal to free float.
• Free float can never be more than total float.
• Activities connected in a sequence often share the same total float, depending on their logic relationships.
• If total float is negative, the project is already off track and won’t meet its deadline without adjustments.

Understanding how to interpret total float helps you see where you’ve got flexibility—and where even a small delay could cause big problems. If you want to pass the exam, and manage projects without constant fire drills, learn the difference between free float and total float, master the formulas, and get familiar with how they show up in network diagrams. It’s not just theory. It’s how you stay in control when your project starts pushing back.

Understanding and Using Free Float

Free float is how much time is available in the schedule without risk before impacting other project activities. In laymen’s terms, how long can there be a delay before there is a problem (including costs or delays on the overall effort). Free float is only present when two or more activities share a common successor, which on a network diagram appears as a convergence.

Free Float Defined

Free float only applies to activities not on the critical path; in other words, the delay is “free” of impact on other activities.

FREE FLOAT

The amount of time a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint – Source PMI.org Lexicon https://www.pmi.org/pmbok-guide-standards/lexicon

Free float is about flexibility. Project Managers and those working to earn a PMP® certification know one core responsibility is knowing when the work will be done. Float is part of the network diagram used to map out activity duration.

Free Float Formula

Unlike some project calculations that make your head spin, figuring out free float is refreshingly simple. It just takes one quick subtraction:

Free Float = ES of next activity – EF of current activity

That’s it. No complex math—just two numbers and a straight answer.

Free float only applies to activities that aren’t on the critical path. It shows how much a task can be delayed without delaying the early start of the next task in the sequence. If an activity is critical to reaching the project’s finish date, it won’t have any free float.

Free Float Example

Let’s say Activity A finishes on Day 5, and Activity B—which depends on A—starts on Day 7.

Using the formula:
Free Float = ES of next activity – EF of current activity
Free Float = 7 – 5 = 2 days

That means you can delay Activity A by up to 2 days without affecting the start of Activity B. That’s your free float.

Even if you’re using scheduling software, you still need to understand how free float is calculated. It helps you catch errors and explain your timeline clearly to stakeholders. Once all float values are calculated, the critical path becomes clear—those activities with zero float. Delay them, and you delay the entire project.

Understanding and Using Total Float

Informally called “total float PMP,” the calculation for the overall path duration happens when within a network diagram there are multiple paths to completion.  The PMI’s A Guide to Project Management Body of Knowledge (PMBOK® Guide) uses day one of the project as one. As with free float, total float is within the critical path scheduling technique including network diagrams.

Total Float Defined

Those with a PMP® certification, know total float is looking at the impact a delayed activity can have on the overall project duration. It is shared among all activities in a sequence.

TOTAL FLOAT

The amount of time a schedule activity can be delayed or extended from its early start date without delaying the project finish date or violating a schedule constraint. – Source PMI.org Lexicon https://www.pmi.org/pmbok-guide-standards/lexicon

It can be a little confusing in that total float may be referred to as simply “float” or “slack.” For the PMP® certification exam, use the official PMI® definition and formula for total float when asked about float.  

Total Float Formula

You can use either of these formulas:

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

Where:

• ES = Early Start
• LS = Late Start
• EF = Early Finish
• LF = Late Finish

Total float is a vital number for managing flexibility within a schedule. Here’s what you need to know:

• Every activity has its own total float value.
• Total float is always greater than or equal to free float.
• Free float can never exceed total float.
• Activities linked in a sequence often share the same total float, depending on logic ties.
• If total float is negative, the project is already behind. You’ll need to adjust durations or dependencies to meet the deadline.

Understanding how to calculate and interpret total float helps you stay in control—especially when resources are tight and deadlines are non-negotiable.

Total Float Example

Let’s walk through a simplified example based on a network diagram from izenbridge.com. The project includes multiple paths from start to finish:

• Path 1: A → C → E
• Path 2: B → C → E
• Path 3: B → D → E

Out of these, Path ACE is the critical path with a total duration of 18 days. Since it’s the longest path, it has zero total float—any delay on this path will delay the entire project. That means Activities A, C, and E have no float—they must happen exactly as scheduled.

Now let’s look at the other activities:

• Activity B has a total float of 1 day, meaning it can be delayed by one day without affecting the project’s end date.
• Activity D has a total float of 6 days, giving you more room to shift or delay that task if needed.

One important takeaway: don’t assume a task has only one direction or dependency. In this case, Activity B can flow either to C or D, depending on the path. A quick glance might suggest there are only two paths, but the branching from Activity B creates a third. That’s why careful analysis of your network diagram is critical to identifying all possible paths and calculating total float correctly.

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Understanding and Using Project Float

Within project schedule work, there is a third float concept known as “project float” which looks at the overall project impact of delays. Currently, project float is not included in the PMI’s online lexicon yet can be found in other project reference sources.

Project Float Defined

Interestingly, project float connects to the commitment of the project manager for a specific completion target. Whereas free and total float are about the time an activity can be delayed, project float is the time of delay based on imposed deadlines.

PROJECT FLOAT

Amount of time a project can be delayed without impacting an imposed deadline or commitment by the project manager

Depending on the work environment, a project may have an imposed deadline to be complete before a holiday or to align with the sales team’s new marketing campaign.

Project Float Formula

Project float is determined by subtracting the planned finish date from the imposed deadline. And with it being an imposed deadline, it may be something that changes outside of the project.

Project Float = Imposed Deadline – Planned Finish Date

For example, a CEO may say the project deadline is December 15^th, to occur before employees leave for a year-end holiday. However, the CFO needs to close out the financials for the year and thus imposes a deadline of December 1^st, which the CEO approves. This imposed deadline is not determined within the project itself but is imposed on the project by outside forces.

Comparing Float: Free Float vs Total Float

No serious discussion of float is complete without a head-to-head look at free float vs total float—especially if you’re preparing for the PMP® certification exam.

According to PMI’s Critical Path Method Calculations white paper and insights from the Deep Fried Brain project blog, here’s what you need to keep in mind:

• Free Float is the amount of time a task can be delayed without delaying the early start of its immediate successor.
• Total Float is the amount of time a task can be delayed without delaying the project’s overall completion date.

Both types of float are crucial in schedule planning, but they serve different purposes. For the exam, make sure you understand how each is calculated, when each applies, and how they relate to the critical path. Recognizing these differences can help you avoid common traps and correctly interpret network diagrams under pressure.

PMP® Certification Exam Float Question Examples

Question	A	B	C	D
You are in the process of executing your project and need to know when it will be completed. You have the following activity durations on your project: A=8, B=14, C=6, D=6, E=12, F=6. You also know that D is dependent on A and B. Task F is a successor of D and E. Task C is a predecessor of task E. Based on this information what is the critical path and what is the float of task A?	Critical path is BDF and the float of task A is 6	Critical path is ADF and the float of task A is 0	Critical path is CEF and the float of task A is 0	Critical path is BDF and the float of task A is 2
An externally imposed project completion time sets the project duration at 75 days. The critical path of the project is established as 75 days, with a standard deviation of 3 days. What could be the maximum project float available?	Six days	Zero days	Three days	Cannot be established
The sponsor wants the project completed in 40 days. The CPI is 1.1 and the project critical path duration is 38 days with a standard deviation of two days. What is the maximum project float?	Eight days	Two days	Zero days	Four days

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Answers

1. A. For this question you need to draw out the schedule network diagram based on the information provided. You would have the following paths: A to D, B to D, C to E, D to F and E to F. You would then need to use the durations provided to do a forward and backwards path analysis. The end result is that the critical path is BDF and the float of task A is 6.
2. C. Project float is the difference between an externally-imposed completion period and estimated project duration, which is equal to the length of the critical path. The difference is zero. Add to this the standard deviation of 3 days (implying that the critical path could be +/- 3 days from the estimated one). The maximum float could be 0+3 = 3 days.
3. D. Project float is defined as the variance between the critical path duration (38 days) and the sponsor imposed duration (40 days). However, in this case we have standard deviation as an additional consideration. Since the standard deviation is +/- 2 days our critical path duration can actually be between 36 and 40 days (i.e. 38 +/- 2). Knowing we could have a critical path of 36 days against the imposed sponsor constraint date (40 days), we therefore have a maximum project float = 4 days.

Conclusion

Project schedules vary in complexity and in what can impact the final duration. Project managers need to understand float within the Critical Path Methodology for the PMP® certification exam and as a means to better manage a schedule.