Free float measures how long an activity can slip without delaying an immediate successor. Total float measures how long it can slip without delaying the project finish or another controlling target date. That is the essential difference in the free float vs total float comparison.
Total float helps schedulers identify critical and near-critical paths. Free float provides a more local view of flexibility between linked activities. Therefore, the two values answer different management questions and should not be used interchangeably.
Free Float vs Total Float at a Glance
- Free float: The time available before an activity delay affects the early timing of a successor.
- Total float: The time available before an activity delay affects the project completion date or another date controlling the backward pass.
- Primary use of free float: Evaluating local handoffs, resource movement and short-term resequencing.
- Primary use of total float: Identifying criticality, monitoring schedule margin and prioritizing management attention.
- Effect of using free float: A delay within free float does not move the successor’s early dates.
- Effect of using total float: A delay may move one or more successors even though the project finish remains unchanged.
- Ownership: Free float applies to a specific activity and its successor relationships. Total float is shared by activities along a network path.
The GAO Schedule Assessment Guide describes total and free float as indicators of schedule flexibility. It also emphasizes that total float is shared along a sequence of activities rather than reserved for one activity or control account.
What Is Total Float?
Total float is the amount of time an activity can be delayed or extended before the delay affects the program’s finish date. Depending on the network and scheduling settings, it may also reflect an interim target, deadline or constrained milestone.
In a conventional Critical Path Method (CPM) calculation, total float derives from the difference between an activity’s early and late dates:
- Total float = late start minus early start
- Total float = late finish minus early finish
The scheduling engine calculates early dates during the forward pass and late dates during the backward pass. Calendars, relationship types, lags, constraints, progress and target dates can affect the result. For a deeper discussion, see what total float means in project scheduling.
How to interpret total float
- Positive total float indicates some calculated flexibility before the controlling completion date is affected.
- Zero total float indicates no calculated flexibility. A day of additional delay will generally transfer to the controlling finish date.
- Negative total float indicates that the calculated schedule extends beyond a constraint, deadline or required completion date.
Negative float is not extra work or a reserve held by management. Instead, it quantifies a schedule conflict. The program must recover the indicated time, revise the plan or change the controlling date through an authorized process. See what causes negative float for a focused explanation.
What Is Free Float?
Free float is the amount of time an activity can move later without delaying the early date of an immediate successor. It evaluates flexibility at the next network handoff rather than at the project finish.
For a simple finish-to-start relationship with no lag, free float is the working-time gap between the predecessor’s early finish and the successor’s early start. However, relationship types, lags and different calendars make the detailed calculation more complex. The scheduling application should perform that calculation.
The Microsoft Project FreeSlack definition describes free slack as the time a task can be delayed without delaying successor tasks. Deltek Open Plan uses the same basic concept in its float calculation documentation.
Why zero free float does not make an activity critical
An activity can have zero free float and still have substantial total float. In that case, any delay will move its successor, but the connected path can still absorb the delay before project completion moves.
Therefore, schedulers should not identify the critical path by filtering for zero free float. Criticality is normally evaluated through total float, longest-path analysis and the logic driving the relevant completion milestone. The complete method is covered in the Critical Path Method guide for program schedulers.
A Practical Free Float vs Total Float Example
Consider a fictional avionics development program with this branch of work:
- Complete interface control document
- Release environmental test procedure
- Conduct qualification readiness review
- Join the main integration path
Assume the branch can finish eight working days later without delaying the integration milestone. As a result, all remaining activities on the branch have eight days of total float at the start of the analysis.
The interface document has zero free float because the test procedure starts as soon as the document finishes. If the document slips three days, the test procedure also moves three days. However, the integration milestone does not move because the branch has enough total float.
The qualification readiness review sits at the end of the branch and can move eight days before it affects the main integration path. Therefore, it has eight days of free float and eight days of total float.
- Interface document: 0 days free float and 8 days total float.
- Readiness review: 8 days free float and 8 days total float.
If the interface document consumes three days, it shifts the downstream branch and leaves five days of total float. The first activity did not own all eight days. Instead, it consumed three days of flexibility shared by the path.
Why Schedulers Need Both Values
Total float supports path-level decisions
Total float shows which paths have the least remaining flexibility. Consequently, it helps program managers and control account managers (CAMs) focus on activities most likely to affect major milestones or program completion.
Schedulers often sort incomplete activities by total float and then trace the lowest-float paths. However, a numerical sort does not replace logic analysis. Constraints, open ends, excessive lags and invalid status can produce misleading float values.
Near-critical work also deserves attention because minor delays can cause a path to overtake the current critical path. A structured approach appears in near-critical path schedule monitoring.
Free float supports local execution decisions
Free float helps the team understand whether moving one activity will disturb an immediate handoff. For example, a functional manager may want to move a test engineer to higher-priority work for three days. An activity with at least three days of free float may accommodate that change without shifting any downstream early dates.
By contrast, an activity with total float but no free float requires more coordination. Moving it will also move one or more successors, resource assignments and planned handoffs, even if the final delivery date remains unchanged.
Float Is Calculated Flexibility, Not Contingency
Teams sometimes treat positive total float as a funded reserve or a block of time assigned to an activity owner. That interpretation is incorrect. Float results from the current network logic, durations, calendars and date controls. It will change when any of those inputs change.
In addition, multiple activities along a path share total float. If an early activity consumes five days, downstream activities may lose the same five days. A CAM should not assume that the total float shown on an activity remains available regardless of earlier performance.
Free float is less disruptive to consume because it does not move immediate successor dates. Even so, it is not permanent. Status updates, revised logic, actual dates and resource-driven changes can reduce or eliminate it.
How Float Appears in Microsoft Project and Deltek Open Plan
Microsoft Project
Microsoft Project generally uses the term slack rather than float. The relevant fields are Free Slack and Total Slack. Microsoft’s TotalSlack documentation defines total slack as the time a task can be delayed without delaying the project’s finish date.
A practical schedule review should display both fields beside early and late dates. Also inspect task constraints, deadlines, calendars and successor logic before accepting the values. A task with zero total slack may be critical, but the scheduler should still confirm that it lies on a continuous driving path to the milestone under review.
Deltek Open Plan
Deltek Open Plan calculates total float and free float during time analysis. Its documentation defines total float as the difference between early and late start dates, measured in working periods of the activity calendar. It defines free float as the maximum delay beyond early dates that will not move any successor beyond its early dates.
Open Plan can also calculate relationship float and specialized float values. Therefore, users should verify which field appears in an export, report or schedule quality tool rather than assuming every field labeled “float” represents activity total float.
Float in an IMS and EVMS Environment
In an Integrated Master Schedule (IMS), total float helps the program identify paths that threaten contractual deliveries, technical events and major integration milestones. Free float helps planners evaluate handoffs between teams and determine where limited resources can move with the least disruption.
However, accurate float depends on a credible network. Missing predecessors or successors, incorrect relationship types, excessive constraints and incomplete status can invalidate the calculation. These defects also weaken critical path analysis. See how to perform critical path analysis in an IMS for a broader review process.
Float terminology is not, by itself, a universal contractual reporting requirement. For contracts that include FAR 52.234-4, Earned Value Management System, the contractor must use the required Earned Value Management System (EVMS) and submit reports required by that contract. The exact schedule fields and reporting rules depend on the solicitation, contract, Contract Data Requirements List, applicable data item descriptions, agency procedures and negotiated tailoring.
Likewise, the GAO Schedule Assessment Guide presents schedule assessment best practices. It does not replace contract terms or agency policy. Program teams should separate useful scheduling practice from a binding requirement.
Common Float Analysis Mistakes
- Using free float to identify the critical path: Zero free float only indicates that a successor will move. It does not prove that project completion will move.
- Assuming each activity owns its total float: Activities on the same path usually share the available total float.
- Treating all positive float as valid: Excessive float may indicate missing logic, open ends or a distant constrained completion milestone.
- Ignoring calendars: Float is measured in working time. Two activities can show different results because they use different calendars.
- Confusing nonworking time with float: Weekends, holidays and shift breaks define availability. They do not automatically create schedule flexibility.
- Ignoring constraints and deadlines: These date controls can change the backward pass, create negative float or obscure the natural longest path.
- Reporting float without a milestone reference: Management needs to know whether the value relates to program completion, a contractual delivery or an interim event.
- Analyzing stale values: Float should be recalculated after status, logic or calendar changes.
A Practical Float Review Sequence
- Confirm the status date and recalculate the schedule. Float based on outdated status has little management value.
- Check incomplete activities for missing logic. Open ends often create unrealistic float.
- Review constraints, deadlines and target dates. Determine which dates control the backward pass.
- Sort incomplete activities by total float. Trace the lowest values to the relevant completion milestone.
- Compare free float with total float. Activities with total float but no free float require downstream coordination if moved.
- Investigate unusually high or rapidly changing values. Confirm that the displayed flexibility reflects the execution plan.
- Discuss float consumption with activity owners. Focus on path-level consequences rather than treating float as an individual allowance.
- Document material findings. Explain negative float, excessive float and corrective actions in schedule analysis narratives when required.
Frequently Asked Questions
Can free float be greater than total float?
Under ordinary CPM conditions, free float should not exceed total float. If a tool appears to show the opposite, review calendars, date constraints, target dates, relationship settings and the exact fields being compared.
Can an activity have total float but no free float?
Yes. The activity can delay its successor immediately while the overall path still has enough flexibility to protect the project finish. This condition is common in chains of linked activities.
Which float should management monitor?
Management should use total float to monitor critical and near-critical paths. Schedulers should also use free float when evaluating local handoffs, resource movement and short-term execution options.
Does positive total float prove the schedule is healthy?
No. Positive float may represent valid flexibility, but it may also result from missing logic, weak integration or distant date constraints. The scheduler must test the reasonableness of the value against the actual execution plan.
The Bottom Line
The free float vs total float distinction comes down to the date affected by a delay. Free float protects the immediate successor’s early timing. Total float protects the controlling project or milestone finish date.
Use total float to understand path criticality and remaining schedule flexibility. Use free float to understand whether a local change will disturb downstream work. Finally, validate both values against network logic, calendars, constraints and current status before using them to make program decisions.