A common question we get is: What’s the difference between Total Float and Free Float? Primavera P6 calculates both automatically every time you run a schedule. While most schedulers prioritize Total Float, understanding Free Float unlocks flexibility for field operations.
Schedulers gravitate to total float in P6 because it appears in the “classic” schedule layout project layout file (PLF), which comes standard with P6 when the sample data is loaded during installation. These standard layouts show a Total Float column, which is automatically populated after the project is scheduled.
Free float resides in P6’s model data but stays hidden in classic PLFs. That’s why new schedulers often overlook it, sticking solely to visible total float without leveraging its helpful sibling, a more localized measure of scheduling leverage: free float.
Here, we examine why the hidden Free Float column deserves attention equal to Total Float—for unlocking true field flexibility.
How P6 Calculates Float: The Forward and Backward Pass
Every time you schedule a project in P6 (Fn+F9 or Schedule from the Tools menu), P6 runs two passes through your network.
- The forward pass calculates the Early Start (ES) and Early Finish (EF) of every activity. It does this by working from the project start forward through all dependencies.
- The backward pass calculates the Late Start (LS) and Late Finish (LF) of every activity. This is done by working backward from the project finish (or any imposed ‘Must Finish By’ constraint).
From these four dates, P6 automatically derives both float values.
Total Float = Late Finish − Early Finish (equivalently: LS − ES)
Free Float = Early Start of next activity − Early Finish of this activity
Most P6 schedulers know that if Total Float equals zero, the activity is on the critical path. By default, P6 highlights it in red. If Total Float is negative, you have a constraint violation or a schedule that is already behind its target finish.
Where To Find Each Column in P6
Total Float
Total Float appears in all three standard classic P6 layouts by default. If it’s not visible in your layout or in the activity table, right-click any column header, then from the pop-up menu choose Columns, and in the Columns dialog, Figure 1, select Available Options | Find.
Enter “Total Float” in the Find dialogue, Figure 2, then click the arrow to include it in Selected Options.
Free Float
As mentioned, Free Float is typically not shown in the default layouts. To add it, in the activity table, right-click any column header and from the pop-up menu choose Columns and follow steps as before or in the Columns dialogue’s categorized list of Available Options, expand Durations, select Free Float and click to Add it to the Selected Options, Figure 3.
As you become more familiar with the categories, searching by category, as shown in Figure 3, becomes more efficient and handier.
Total Float in P6
In P6, total float tells you how long an activity can slip before the project finish date (or any ‘Must Finish By’ constraint on a milestone) moves. It is path-level, not task-level.
The critical distinction is that total float is shared by every activity on the same path. If Activities A, B, and C sit on a path with 12 days of total float and a field team uses 10 days on Activity A, when P6 recalculates, it will show only 2 days of total float on B and C. The path is now near-critical, and no one may have flagged it.
Reading Total Float Trends in P6
P6’s schedule comparison feature (Tools | Visualizer click + and then Comparison) lets you track how total float changes between schedule revisions and updates. A helpful practice is to export total float by activity to a spreadsheet after each update and plot the trend. Paths whose total float is shrinking faster than their duration are drifting toward criticality.
Total Float and Constraints in P6
Constraints in P6 directly affect float calculations. For example, a ‘Finish On’ constraint on an intermediate milestone can create a segment of the schedule with its own effective project finish. It will compress the total float across all activities feeding that milestone, independent of the project end date. You should check activities showing unexpectedly low total float and whether an activity constraint is along its path.
Free Float in P6
Free float in P6 is the gap between when an activity finishes (Early Finish) and when its earliest successor can begin (Early Start of that successor). It’s the wiggle room that an activity has before it starts to hold up the next activity in the sequence.
Because free float looks only at the immediate successor relationship, it is always less than or equal to the total float. A common situation in which free float equals total float occurs when an activity feeds directly into the project finish milestone with no successors. In that case, delaying the activity by its free float amount also moves the project end by the same amount.
When Free Float is the Right Metric to Use
- A subcontractor asks if Activity X can finish up to 3 days late without delaying their crew on the successor activity. Check the free float first—if sufficient, approve confidently: the successor’s early start stays protected, no downstream rescheduling is needed.
- A field supervisor wants to shift resources to another activity for two days. In this case, if free float ≥ 2, there is no sequencing impact.
- You are building a look-ahead schedule for the field team and want to show which activities have true individual flexibility without dependencies on path-level float management.
Side-By-Side Comparison
| TOTAL FLOAT IN P6 | FREE FLOAT IN P6 |
| It reflects float to project finish or late constraint. It’s shared along the path and using it on one activity reduces it for successors. | It shows float to earliest successor only. It’s exclusive to the activity and consuming it does not affect any downstream early start. |
| Attribute | Total Float | Free Float |
| Formula | Late Finish − Early Finish | ES (next activity) – EF (this activity) |
| Scope | Project finish or deadline constraint | Earliest immediate successor |
| Shared across path? | Yes – path-level resource | No – exclusive to this activity |
| Drives critical path? | Yes (TF = 0 = critical) | No direct effect |
| Safe for unilateral use? | No – coordinate with scheduler | Yes – no downstream impact |
Using Both Columns Together in Practice
Step 1: Run the schedule (F9) –Before scheduling, confirm the data date is correct and the project has a valid calendar and finish milestone.
Step 2: Check the critical path -Filter activities where Total Float = 0. These are your true critical activities. P6 highlights them red, but the filter gives you a clean list for reporting.
Step 3: Scan near-critical paths -Filter for Total Float ≤ 5 (or 10% of remaining duration). These are the paths most likely to become critical at the next update.
Step 4: Add the Free Float column -For any activity where a team is asking about delay tolerance, check Free Float first. If the requested delay is within Free Float, it’s operationally safe.
Avoid a Common Mistake
One of the most frequent errors we see is treating the Total Float column as a per-activity approval threshold. A project manager sees that Activity D has 15 days of total float and tells the responsible team they can take up to 15 days of schedule slip without consequence. They can’t, and not independently. Activities earlier on that path may already have consumed some of it, or activities downstream may need it for their own resource adjustments.
In P6, only Free Float is truly the activity’s own. Total Float always belongs to the path.
The safest practice is to treat total float as a read-only indicator for path monitoring and use free float as the approval metric for individual activity delays.
Configuring P6 for Better Float Visibility
- Save a layout with both Total Float and Free Float columns visible and share it with the project team as a standard layout.
- Create a filter called “Near-Critical” (Total Float ≥ 0 AND Total Float ≤ 10) and include its output list in weekly schedule review meetings.
- Use the “Define Critical Activities” setting (Schedule Options → Advanced) to adjust whether P6 uses Total Float ≤ 0 or a custom threshold to define tasks as critical and color their activity bars on the Gantt chart red.
- Set a project baseline early and use P6’s variance columns (BL Total Float, BL Free Float) to track float erosion against the original plan.
Primavera P6 computes total float and free float whenever you calculate the schedule, so both are available. The scheduler’s role is to determine when Free Float can be safely consumed for localized, unimpactful delays (such as crew shifts or minor slips) without eroding downstream tasks’ Total Float or causing a project-wide delay.