Free Float vs Total Float: A Complete Guide for Project Managers

Total float is a key concept in Critical Path Analysis (CPA), a project management technique that helps identify critical tasks and their timelines. Total float refers to the amount of time a task can be delayed without affecting the overall project completion date. It is particularly useful for project managers in identifying schedule flexibility and prioritizing tasks.

How to Calculate Total Float

Total float is calculated using the following formula:

Total Float = Late Finish – Early Finish

Where:

• Late Finish is the latest possible date by which an activity can finish without delaying the project.

• Early Finish is the earliest possible date by which an activity can finish.

These values are derived using a critical path method (CPM) or network diagram analysis.

Total Float Example

Consider a project with the following activities and durations:

• Activity A: 5 days

• Activity B: 3 days

• Activity C: 4 days

• Activity D: 2 days

The critical path is A → B → C, with a total duration of 12 days.

The early finish times are:

• Activity A: 0 + 5 = 5

• Activity B: 5 + 3 = 8

• Activity C: 8 + 4 = 12

• Activity D: 8 + 2 = 10

The late finish times are:

• Activity A: 12 – 5 = 7

• Activity B: 7 – 3 = 4

• Activity C: 4 – 4 = 0

• Activity D: 12 – 2 = 10

The total float for each activity is:

• Activity A: 7 – 5 = 2 days

• Activity B: 4 – 8 = -4 days

• Activity C: 0 – 12 = -12 days

• Activity D: 10 – 10 = 0 days

Consider another project:

• Activity X: 6 days

• Activity Y: 4 days

• Activity Z: 3 days

Critical path: X → Y → Z = 13 days

Early finish times:

• Activity X: 0 + 6 = 6

• Activity Y: 6 + 4 = 10

• Activity Z: 10 + 3 = 13

Late finish times:

• Activity X: 13 – 6 = 7

• Activity Y: 7 – 4 = 3

• Activity Z: 3 – 3 = 0

Total float calculations:

• Activity X: 7 – 6 = 1 day

• Activity Y: 3 – 10 = -7 days

• Activity Z: 0 – 13 = -13 days

These examples highlight how total float can be positive, zero, or negative, depending on task dependencies and project constraints.

Understanding Free Float

Free float represents the amount of time a task can be delayed without affecting the early start of its immediate successor. It provides insight into localized scheduling flexibility within a sequence of tasks.

How to Calculate Free Float

Free Float = Early Start of Successor Activity – Early Finish of Current Activity

Where:

• The Early Start of the successor is the earliest possible start time of the following activity.

• Early Finish of the current activity is the earliest possible finish time of the task in question.

Free Float Example

Consider a project with the following structure:

• Activity A: 5 days

• Activity B: 3 days

• Activity C: 4 days

• Activity D: 2 days

Critical path: A → B → C = 12 days

Early finish values:

• Activity A: 0 + 5 = 5

• Activity B: 5 + 3 = 8

• Activity C: 8 + 4 = 12

• Activity D: 8 + 2 = 10

Early start values:

• Activity B: 5

• Activity C: 8

• Activity D: 8

Free float calculations:

• Activity A: 5 (Early Finish) → 5 (Early Start of B) = 0

• Activity B: 8 (Early Finish) → 8 (Early Start of C) = 0

• Activity C: 12 (Early Finish) → N/A (no successor) = N/A

• Activity D: 10 (Early Finish) → N/A = N/A

Another project:

• Activity X: 6 days

• Activity Y: 4 days

• Activity Z: 3 days

Critical path: X → Y → Z = 13 days

Early finish values:

• X: 0 + 6 = 6

• Y: 6 + 4 = 10

• Z: 10 + 3 = 13

Early start of successors:

• Y starts at 6

• Z starts at 10

Free float:

• Activity X: 6 – 6 = 0

• Activity Y: 10 – 10 = 0

• Activity Z: No successor = N/A

These examples demonstrate that free float is often zero on the critical path and is only applicable when there are immediate successors.

Difference Between Total Float and Free Float

The main distinction between total float and free float lies in their implications:

• Total float is the amount of time an activity can be delayed without delaying the overall project.

• Free float is the amount of time an activity can be delayed without delaying the start of its next activity.

Illustrative Comparison

Assume a sequence of tasks:

• Task A: 2 days

• Task B: 3 days

• Task C: 5 days

If Task A starts on Monday and ends on Tuesday, Task B starts on Wednesday and ends on Friday, and Task C starts on Saturday and ends the next Wednesday.

• Total Float of Task A = 0 (any delay impacts the project)

• Free Float of Task A = 1 (it can be delayed by one day without affecting Task B’s start)

• Total Float of Task B = 2 (it can be delayed by two days without delaying the project)

• Free Float of Task B = 0 (it directly affects Task C)

• Free Float of Task C = 0 (last task, any delay impacts the project)

Final Thoughts

Both total float and free float are essential tools in project time management. Understanding their differences allows project managers to allocate resources more efficiently and identify which activities require closer monitoring. High total float values suggest flexibility within the overall project, while high free float values indicate flexibility between dependent tasks.

Additional Concepts in Time Management

Duration vs Effort

Effort refers to the total amount of labor required to complete a task, typically measured in person-hours, person-days, or person-months. Duration refers to the actual period over which the task is carried out, from start to finish, irrespective of the number of people working.

Example:

If a task takes 4 hours of effort and only one hour is contributed each day, the duration is 4 days, while the effort remains 4 hours.

Crashing vs Fast Tracking

Crashing involves adding resources to shorten the duration of activities without changing their sequence. Fast tracking involves performing tasks in parallel that were initially scheduled in sequence. Both methods are used to reduce project timelines but come with risks such as increased cost or project complexity.

Total Float vs Free Float in Project Management

Introduction

Project schedules involve multiple tasks with varying degrees of flexibility. Understanding how much flexibility exists for each task is crucial to meeting deadlines and managing resources. Two core concepts that help define this flexibility are total float and free float. Both are vital to the effective management of time within a project, but they serve different purposes and are used in distinct contexts. This article will provide a comprehensive explanation of total float and free float, illustrate how to calculate them, and explain their practical significance in project management.

What is Total Float

Total float, also referred to as slack, represents the amount of time a task can be delayed without delaying the project’s overall completion date. It is a scheduling buffer that allows project managers to prioritize tasks more effectively. Tasks with high total float can be postponed without major consequences, while tasks with zero total float are on the critical path and must be executed as planned to keep the project on schedule.

Understanding total float allows project managers to make better decisions about resource allocation, identify scheduling flexibility, and assess the overall health of the project timeline.

Total Float Formula

Total float is typically calculated using data from a critical path method (CPM) or network diagram analysis. The standard formula is:

Total Float = Late Finish − Early Finish
or
Total Float = Late Start − Early Start

Where:

• Early Start is the earliest time a task can begin based on the project schedule.

• Late Start is the latest time a task can begin without affecting the final project completion date.

• Early Finish is the earliest time a task can be completed.d

• Late Finish is the latest time a task can be completed without delaying the project.ct

If a task’s total float is zero, it is on the critical path. Delays in these tasks directly impact the project end date.

Example of Total Float

Consider a project with four activities:

• Activity A: 5 days

• Activity B: 3 days

• Activity C: 4 days

• Activity D: 2 days

Assume the following task dependencies:

• Activity A must be completed before Activity B can begin

• Activity B must be completed before Activity C can begin.

• Activity A must also be completed before Activity D can begin.

The critical path would be A → B → C. The total project duration is the sum of durations along this path: 5 + 3 + 4 = 12 days.

Calculate early start and early finish:

• Activity A: ES = 0, EF = 5

• Activity B: ES = 5, EF = 8

• Activity C: ES = 8, EF = 12

• Activity D: ES = 5, EF = 7 (not on the critical path)

Now, calculatethe  late start and late finish based on the project completion date:

• Activity C: LF = 12, LS = 8

• Activity B: LF = 8, LS = 5

• Activity A: LF = 5, LS = 0

• Activity D: As it ends at day 7 and does not affect the final project date, LF = 12, LS = 10

Calculate total float:

• Activity A: LS – ES = 0

• Activity B: LS – ES = 0

• Activity C: LS – ES = 0

• Activity D: LS – ES = 10 – 5 = 5

In this example, Activity D has a total float of 5 days, which means it can be delayed by up to 5 days without affecting the project timeline. Activities A, B, and C are on the critical path and have no float.

Importance of Total Float

Understanding and managing total float helps project managers in the following ways:

• Identify critical activities that must stay on schedule

• Allow flexibility for non-critical activities.

• Optimize resource allocation by focusing attention on tasks with limited flexibility.

• Improve decision-making when delays or issues occur.r

Total float is especially useful when managing complex projects with many interdependent activities. It provides clarity about which tasks can be delayed and which cannot.

What is Free Float

Free float is the amount of time a task can be delayed without delaying the start of its immediate successor. Unlike total float, which considers the overall project completion, free float is limited to the local relationship between a task and the next activity in sequence.

Free float is particularly helpful when managing task sequences where a delay in one task may or may not impact the start of the next. It gives project managers a more granular view of schedule flexibility at the task level.

Free Float Formula

The formula for free float is:

Free Float = Earliest Start of Next Activity − Early Finish of Current Activity

WhereThe :

• Earliest Start of the next activity is when the succeeding task is scheduled to begin.

• Early Finish of the current activity is when the current task is scheduled to be completed.d

If free float is zero, the successor must begin as soon as the current task ends. If there is a gap, the task has some free float and can be delayed without affecting the successor.

Example of Free Float

Using the same project:

• Activity A: 5 days

• Activity B: 3 days

• Activity C: 4 days

• Activity D: 2 days

Dependencies:

• A → B → C

• A → D

From earlier, we have:

• EF of Activity A = 5

• ES of Activity B = 5

• EF of Activity B = 8

• ES of Activity C = 8

• EF of Activity D = 7

Free float for each:

• Activity A: ES of B – EF of A = 5 – 5 = 0

• Activity B: ES of C – EF of B = 8 – 8 = 0

• Activity D: No successor = Free Float is total float = 5

This shows that Activities A and B have no free float, indicating that any delay would delay the successor. Activity D, being independent, has a free float equal to its total float.

Key Differences Between Total Float and Free Float

While both total float and free float represent available time flexibility in scheduling, they differ in their scope, purpose, and impact on project timelines.

Scope of Impact

Total float affects the entire project schedule. A task with zero total float cannot be delayed without delaying the project’s completion. Therefore, managing total float is critical for ensuring timely project delivery.

Free float is more localized. It deals only with the immediate successor activity. Even if a task has free float, a delay may not impact the overall schedule unless it is also on the critical path. Free float is ideal for managing dependencies at the task level.

Relationship to Critical Path

Total float is directly related to the critical path. Tasks on the critical path will always have zero total float. Identifying these tasks is essential for prioritizing resources and avoiding delays.

Free float may or may not be zero for tasks on the critical path. A task can have zero total float but still have free float if there is a lag between its completion and the start of its successor.

Scheduling Flexibility

Total float provides more comprehensive information about task scheduling flexibility. It helps in identifying where adjustments can be made without compromising the project end date.

Free float is narrower and gives insight into how a delay in one task might affect the next. This is useful in resource leveling and short-term planning.

Usage in Project Monitoring

Project managers use total float to identify which tasks can be safely delayed and which require immediate attention. It helps in updating schedules and forecasting potential risks.

Free float is often used by team leads or task managers to understand dependency-related constraints. It can assist in managing hand-offs between teams or departments.

Practical Applications of Float in Project Management

Understanding and utilizing float can significantly enhance project execution. Here are key practical applications.

Resource Allocation

Total float helps project managers assign resources efficiently. Tasks with higher float can be scheduled around more constrained activities, improving resource utilization and avoiding bottlenecks.

For example, if two tasks require the same specialist and one has a float of five days while the other is on the critical path, assigning the specialist to the critical task first will prevent delays.

Risk Management

Knowing where float exists helps in identifying areas where buffers can absorb unexpected delays. Tasks with little or no float are high-risk and need constant monitoring. Risks affecting such tasks must be mitigated through contingency planning.

Schedule Optimization

Free float allows for micro-optimization of the schedule. If a task can be delayed slightly without affecting the next one, project managers can stagger starts to better align resources or accommodate changes without affecting the overall schedule.

Change Management

When scope changes occur, understanding float helps in evaluating the impact. If changes affect tasks with float, the overall timeline may not shift. This flexibility aids in stakeholder communication and scope negotiation.

Managing Float in Project Software Tools

Most modern project management software tools like Microsoft Project, Primavera P6, and others automatically calculate float values. These tools use critical path analysis and network logic to derive float values, update them dynamically, and visually represent them in Gantt charts or network diagrams.

Float Visibility

Tasks with zero total float are typically highlighted in red on Gantt charts, indicating their presence on the critical path. Other tasks show float as a visual buffer in their timelines.

Float Constraints

Project managers can set constraints or float limits to ensure that tasks with a certain buffer are addressed within acceptable margins. This is particularly useful in large projects where tasks are managed by different teams.

Float-Based Filtering

Filtering tasks by float can help prioritize efforts. For instance, project teams can filter tasks with less than two days of total float and closely monitor them for signs of slippage.

Common Misconceptions About Float

There are several misunderstandings that project managers and teams may have regarding float. Clarifying these misconceptions is essential to effective project execution.

Float Means Unimportant

Just because a task has float does not mean it is less important. Tasks with float can become critical if earlier activities slip or if scope changes consume available float. Every task should be tracked, even those with significant float.

Float is Always Positive

Float can be negative. Negative float occurs when the schedule is not feasible based on constraints or deadlines. This signals an immediate issue that must be resolved through schedule adjustments, resource reallocation, or scope changes.

Float is Static

Float is dynamic and changes as the project progresses. As tasks are completed, delayed, or adjusted, the float values update. A task that had five days of float may have only one after a delay upstream.

Advanced Concepts Related to Float

Project scheduling involves more than just total and free float. Related concepts further enhance the understanding of task timing and flexibility.

Negative Float

Negative float occurs when a task is scheduled to finish after its latest allowable finish date. This typically indicates a constraint violation and suggests that corrective action is required. Negative float often appears when external deadlines are added that are incompatible with the rest of the schedule.

Critical Chain and Buffer Management

Critical chain project management (CCPM) goes beyond float and introduces buffers. Rather than distributing float across individual tasks, CCPM aggregates buffer time at the end of task sequences or the project. This reduces Parkinson’s Law and improves schedule reliability.

Crashing and Fast Tracking

When float is insufficient or negative, project managers may use techniques such as crashing or fast tracking:

• Crashing involves adding extra resources to critical path tasks to shorten duration. This reduces float and often increases cost.

• Fast tracking involves performing tasks in parallel that were originally scheduled in sequence. This increases risk but can help meet deadlines.

These techniques affect float and should be used carefully after evaluating their impact on the project’s risk profile.

Effort vs Duration

Understanding the difference between effort and duration is key when analyzing float. Effort refers to the amount of work needed to complete a task, while duration is the calendar time over which the task is scheduled.

Float calculations are based on duration, not effort. A task may require 20 hours of effort but be scheduled over 5 days. If the schedule allows only 3 days, then float becomes negative unless additional resources are applied.

Visualizing Float in Network Diagrams

Network diagrams are a common method for visualizing float. Each task is represented as a node with arrows indicating dependencies. Critical paths are highlighted, and float values are indicated within each node.

For instance:

• A node for Task A might show ES = 0, EF = 5, LS = 0, LF = 5, Total Float = 0

• A node for Task D might show ES = 5, EF = 7, LS = 10, LF = 12, Total Float = 5

These visuals help teams immediately identify where float exists and where it does not. Project reviews using network diagrams allow for quick decision-making and more transparent planning discussions.

How Float Impacts Risk Management and Resource Leveling

Understanding float is essential not just for schedule flexibility, but also for advanced project control techniques such as risk management and resource leveling. Float—whether total or free—can be a key buffer against project uncertainties and resource constraints. In this section, we explore how float influences these two critical areas.

Float and Risk Management

Risk management involves identifying, assessing, and controlling risks that may affect a project’s objectives. Float provides a built-in time cushion that helps mitigate schedule-related risks without affecting the overall project deadline.

Float as a Schedule Buffer

Float acts as a buffer between activities, absorbing potential delays without impacting subsequent tasks or the project completion date. When properly managed, float enables teams to accommodate unforeseen events like:

• Vendor delays

• Weather disruptions

• Team member unavailability

• Technical issues

For example, if Activity B has a total float of 5 days, it can be delayed by up to 5 days without delaying the project. This allows project managers to reallocate attention or resources to more critical activities without jeopardizing the overall timeline.

Float Analysis in Risk Response Planning

Project managers often conduct a float analysis to identify which tasks are most susceptible to delays. Activities with zero or negative float are part of the critical path and have no room for delay, making them high-risk. On the other hand, activities with higher float values offer flexibility and are less risky.

This insight helps determine:

• Where contingency plans are necessary

• Which tasks should be monitored closely?

• Where to apply schedule compression techniques

Integration with Schedule Risk Analysis

Advanced risk management tools like Monte Carlo simulations often incorporate float into probabilistic forecasting. These simulations analyze how likely it is for a project to meet its deadline based on float distribution, potential risks, and task uncertainties.

Float and Resource Leveling

Resource leveling is the process of adjusting the project schedule to address resource constraints without changing the project scope. Float plays a crucial role in making this possible.

Using Float for Workload Balancing

In many projects, resources like labor, equipment, or materials are limited and shared across tasks. Overloading a resource on overlapping tasks can lead to burnout, inefficiency, or increased costs.

Float helps address this by allowing non-critical tasks with available float to be rescheduled without impacting the overall timeline. For example:

• If two tasks require the same team and one has 4 days of total float, the task with float can be delayed to free up the team for more urgent work.

• Free float can be used to move tasks within a logical window without affecting successor activities.

This flexibility ensures resources are utilized more effectively and reduces the risk of over-allocation.

Float in Automated Resource Leveling Tools

Many modern project scheduling tools use float as a key parameter in automatic resource leveling algorithms. These systems:

• Detect overloaded resources

• Identify tasks with available float.

• Adjust the schedule to reduce overuse while maintaining deadlines.

This is especially useful in large or complex projects where manual adjustments are inefficient or error-prone.

Float Limits and Leveling Priorities

While float enables resource leveling, it’s not unlimited. Managers must set clear priorities:

• Tasks on the critical path take precedence

• Tasks with more float offer greater flexibility

• Dependencies must still be respected.

Leveling based purely on float without considering task dependencies or priorities can lead to suboptimal results. Therefore, float should be used judiciously in combination with other planning tools.

Strategic Use of Float in Risk and Resource Plans

Float is most effective when it is intentionally planned and tracked. Project managers often take these steps to integrate float into risk and resource strategies:

• Baseline the float at the project start to monitor changes over time

• Avoid using float early unless necessary to preserve schedule flexibility.

• Assign float ownership, especially in large projects, so it is not unintentionally consumed.d

• Track float erosion, a sign that delays are accumulating and risk is increasing

These proactive steps allow float to act as a strategic asset instead of a hidden liability.

Real-World Application of Float: Case Study on Risk Mitigation and Resource Optimization

Float is not merely a theoretical construct in project scheduling; it has practical implications that can significantly influence the success or failure of real-world projects. In this section, we explore a case study that illustrates how project managers use float to manage risks and optimize resource allocation.

Case Study Background: Commercial Office Building Project

Consider a large-scale commercial construction project involving the development of a multi-story office building. The project schedule consists of over 150 activities, including foundation work, structural framing, mechanical and electrical installations, inspections, and interior finishing.

The project duration is set at 18 months, with tight deadlines and multiple subcontractors. The project team uses a Critical Path Method (CPM) schedule in conjunction with project management software that tracks total float and free float for each activity.

Initial Float Assessment and Risk Identification

During the planning phase, the project manager and scheduler identify the critical path, which includes excavation, concrete pouring, structural framing, and roofing. These tasks have zero float, meaning any delay in them will directly impact the project completion date.

However, other activities such as landscaping, non-structural interior work, and signage installation have floats ranging from 10 to 20 working days. These float values are documented during the schedule review.

Simultaneously, a risk assessment highlights the following threats:

• Weather delays affecting exterior work

• Labor shortages due to competing construction projects in the region

• Equipment availability conflicts, especially for cranes and HVAC tools

The project manager decides to leverage available float to mitigate these risks.

Using Float to Mitigate Weather Risks

Excavation and foundation activities are scheduled during the rainy season. Although these are on the critical path, float in related follow-up activitie,s like parking lot paving, is used to adjust the schedule. Instead of beginning paving immediately after foundation work, the team delays this task by 10 days to align with drier weather.

Because parking lot paving had 12 days of total float, this change does not affect the final completion date. The risk of rework and material waste due to rain is reduced significantly.

Resource Leveling with Float for Equipment Optimization

The project requires a single crane for both structural steel placement and rooftop HVAC unit installation. Initially, both tasks were scheduled close together, creating a resource conflict.

The HVAC installation task had 8 days of total float, and its successor activity—ductwork—also had float. The project manager reschedules HVAC installation to start one week later, allowing uninterrupted crane use for structural work. This eliminates the need to rent a second crane, saving an estimated $40,000.

This resource-leveling decision maintains the overall project schedule and resolves the equipment conflict efficiently by utilizing float.

Monitoring and Managing Float During Execution

As the project progresses, the scheduler monitors float values weekly. By mid-project, several activities have lost some of their float due to minor delays. For example, electrical rough-in work lost 4 of its original 10 float days because of material delivery issues.

Rather than wait for the float to erode completely, the project team decides to expedite drywall delivery—a downstream task—to recover lost time. This proactive monitoring of float as an early warning indicator helps the team stay ahead of risks.

Outcome and Lessons Learned

The project is completed two weeks ahead of schedule and within budget. Key factors contributing to the success include:

• Proactive use of float to absorb delays and adjust to weather conditions

• Strategic resource leveling using float to resolve equipment constraints.

• Regular monitoring of float to detect emerging schedule risks early

This case study illustrates that float is not just a buffer, but a powerful management tool when applied strategically.

Key Takeaways from the Case Study

1. Float enables flexible risk responses: Activities with float can be shifted to avoid risk-prone windows or external uncertainties.

2. Resource conflicts can be resolved without affecting the schedule: Float allows for sequencing adjustments that improve equipment and labor efficiency.

3. Monitoring float is as important as monitoring the critical path: Erosion of float may signal growing schedule risk even before the critical path is affected.