Baseline-to-Current-Schedule Float Erosion

Don’t just see what is critical. Track float erosion to spot tasks in danger of becoming critical or worse. Let’s take a look.

Comparing the current schedule against its baseline is the foundation of schedule performance reporting. By measuring the exact gap between baseline and current dates, a true schedule comparison reveals not just when activities are slipping, but how much valuable float buffer is being eaten away.

Done well, it tells a precise story of how the project has drifted from plan, which paths are tightening and where action is needed before activities go critical. Done poorly, it produces a table of dates that nobody acts on.

This article details why you must inspect your schedule for float erosion and exactly how to investigate it.

The Schedule-Comparison Paradigm

Progress reporting begins the conversation; it tells you what percentage of the work has been completed. An activity that’s 50% complete but two weeks late has certainly made progress, but it is also behind schedule.

Schedule comparison provides deeper insight by showing whether that progress is on time relative to the plan. By showing baseline dates alongside current dates for the same activities and measuring the difference, this comparison answers three questions at once:

Has the activity started or finished later than planned?
Has the forecast completion moved?
And how much of the float buffer between this activity and the project end has been eaten up?

Only a baseline schedule-comparison paradigm reveals the full picture, enabling float-erosion analysis.

💡 The baseline is the reference, not the target. It records what was planned; the current schedule records what is now forecast. The gap between them is variance — and it’s not inherently good or bad until you understand why it exists. An activity finishing 5 days early might reflect great performance, or it might mean the scope was quietly removed. Investigate significant variance in both directions.

Refer to the following article for a primer on P6 Professional baselines:

Primavera P6 Baselines Explained

Creating and Assigning a Baseline

In Figure 1, we have a demonstration schedule.

We want to create a new baseline, assign it, then display it on the Gantt chart.

Follow these steps to create a baseline:

Choose Project | Maintain Baselines

In the Maintain Baselines dialogue, Figure 2, click the + Add button.

In the Add New Baseline dialogue, toggle to ‘save a copy of the project as a new baseline’ and then click OK, Figure 3.

This takes a static picture of your schedule in time and stores it as a baseline.

Click the Copy button to make additional copies of your baseline, Figure 4.

Follow these steps to assign the baseline.

Choose Project | Assign Baselines

In the Assign Baselines dialog box, click to assign the baseline to Project Baseline and Primary Baseline, Figure 5.

The baseline is assigned to the Project Baseline because the System Administrator can lock it, preventing anyone from modifying it. We also assign it to the Primary User Baseline because the Bars feature for defining the Gantt chart graphics comes standard with a bar definition for Primary User Baseline.

Figure 6 displays the Assign Baselines dialog box with our baseline assigned to the Project Baseline and Primary User Baseline.

Follow these steps to display the baseline on the Gantt chart.

Choose View | Bars, then toggle on Primary Baseline, Figure 7.

You will also want to toggle on the Baseline Milestone bar definition.

Figure 8 shows the baseline schedule, with the baseline displayed in yellow on the Gantt chart.

Figure 9 shows the schedule after the first month’s update (M1).

Figure 10 is the schedule after the second month’s update (M2).

Calculate Float Erosion in Excel and Reimport to P6

Follow these steps to calculate Float Erosion in Excel and import it into P6.

Choose Enterprise | User Defined Fields.

Create Activities UDF with Data Type Number, Figure 11.

Confirm or add the following columns to the Activity table:

Total Float

BL Project Total Float

Float Erosion

Figure 12 displays the month two update with these columns included.

Note that the Float Erosion column data fields are currently blank.

Export the schedule to an Excel spreadsheet to create a template.

File | Export | Spreadsheet – (XLSX)

Toggle Activities Export type and Next, Figure 13.

Toggle to Export WELLMONT06-M2 and click Next, Figure 14.

Modify Float Erosion Layout

Make sure to include the columns WBS Code, Activity Name, and Float Erosion, Figure 16.

Save the template to Float Erosion Template, click Next, Figure 17.

Click Finish

Copy Data, a list of the tasks, to an Excel Spreadsheet for Float Erosion computation.

Choose View | Group and Sort By.

Select the Group By field to None, then click OK, Figure 18.

Click Edit | User Preferences and in Time Units turn off labeling for Units Format and Duration Format, Figure 19, (We needed the data field to be numbers and not text).

Select Edit | Select All.

Choose Edit | Copy

Figure 20 displays the list of selected tasks and columns for copying and pasting to the spreadsheet.

Paste into a new Excel spreadsheet.

Figure 21 displays the raw data from P6 in the Excel spreadsheet.

Add the following Excel syntax to the Float Erosion column.

Excel = IF(Status_Cell=”Completed”, 0, BL_Float_Cell – Current_Float_Cell)

Figure 22 displays the spreadsheet with Excel syntax for the Float Erosion column.

Copy Float Erosion values, Figure 23.

Paste into Float Erosion Template, Figure 24.

We want to import the template with updated Float Erosion values back into P6.

Choose File | Import | Spreadsheet – (XLSX).

Import to Update Existing Project, Figure 26.

Choose Import Type > Activities, Figure 27.

Figure 28 displays the updated Wellmont06-M2 schedule.

Choose View | Group and Sort By, Figure 29.

Sort by WBS, and Schedule with Float Erosion displays in Figure 30.

Sort by WBS, and Schedule with Float Erosion — **Figure 30**

Float Erosion Analysis Column Layout

Table 1 provides a breakdown of Float Erosion analysis parameters, their role, and analytical insight.

Table 1 – Float Erosion Relevant Parameters

Parameter	Role	Analytical Insight
Variance – BL Start	Root-Cause Diagnostic	Shows if buffer loss was caused by a late start.
Baseline Project Total Float	Starting Benchmark	Established the original flexibility before progress.
Current Total Float	Live Schedule Status	Shows the remaining flexibility
Float Erosion	Core Metric	Quantifies lost buffer days.

Float Erosion Parameter Output

Figure 31 displays the output of the relevant parameters for the float erosion analysis.

The schedule insight gleaned from the float erosion analysis in Figure 31 is as follows:

W1110, Install Grounding, started 4 days late but only lost 3 days of float. The team managed to recover 1 day of execution time, mitigating the delay. It has a 12-day buffer before it threatens the project completion date.
W1120, Install Bus and Jumpers, started 4 days late and lost 3 days of float. There are 6 days of float left.

The identical float erosion across these two tasks does not imply equal risk. Though the paths deteriorate at the same rate, the current total float column highlights that the Install Bus and Jumpers task is much closer to driving a project delay.

Table 2 displays the Float Erosion Diagnostic Matrix.

Table 2 – P6 Float Erosion Diagnostic Matrix

Variance – BL Project Start	Float Erosion [1]	Interpretation	Action
Negative (- Days) Late Start	None (0 Days)	Full Mitigation: Crew accelerated to absorb 100% of the late start.	Confirm that the accelerated remaining logic is realistic.
Negative (- Days) Late Start	Positive (+ Days)Less than start variance W1110 & W1120 (Lost 3 days vs 4 days late)	Partial Mitigation: Crew accelerated to recover some of the delay. Note: W1120 has higher risk due to lower remaining float (6d vs 12d).	Acknowledge crew recovery. Focus resources on W1120 due to the smaller remaining buffer.
Negative (- Days) Late Start	Positive (+ Days) Equal to start variance	Pure Inherited Delay: Crew executed on pace; delay was entirely upstream.	Investigate the late handoff root cause. Current crew hit baseline targets.
Negative (- Days) Late Start	Positive (+ Days) Greater than start variance	Compounding Delay: Late start worsened by slow production.	Urgent intervention: Check crew sizing and bottlenecks.
Zero (0 Days) On-Time Start	None (0 Days)	Perfect Execution: Task started on time and tracked perfectly to baseline production rates	Maintain current execution strategy.
Zero (0 Days) On-Time Start	Positive (+ Days)	Production Slippage: On-time start, but slow execution.	Review production and downstream impacts.
Positive (+ Days) Early Start	None (0 Days)	Early Execution: Early start; preserved planned pace.	Verify early start logic validity upstream.
Positive (+ Days)Early Start	Positive (+ Days)	Eroded Advantage: Task started early but executed slowly, burning through its early start buffer.	Review productivity; determine why early-start momentum was lost.

[1] Float Erosion is calculated as Baseline Total Float – Current Total Float. A positive value represents the total days of project buffer consumed.

Table 2 displays the Float Erosion Diagnostic Matrix. This table lists the output Variance – BL Project Start alongside the Float Erosion (expressed as days of buffer consumed), how to interpret this data and the required actions to keep the schedule on track.

The P6 Float Erosion Diagnostic Matrix is heavily weighted toward late starts (four scenarios) because they present complex environments where field execution can either mitigate or compound the delay. The matrix isolates the impact of on-time starts (two scenarios) and early starts (two scenarios) to verify that a safe project position is maintained.

Float erosion: the leading indicator

Start and finish variance tells you how far an activity has moved. Float erosion tells you how much protective buffer has been consumed between an activity and the project end date. It’s the most sensitive early warning tool in schedule analysis because it detects tightening paths before they reach zero float.

Float Erosion = BL Total Float − Current Total Float

Positive = float has been consumed (path is tightening).

Negative = float has increased (investigate why).

Table 3 is a breakout of the Float Erosion % Baseline Consumed thresholds.

Table 3 – Float erosion thresholds

% Baseline Consumed	Float Erosion	Interpretation	Action
≤ 25%	Normal	Standard operational drift.	Monitor during routine updates.
> 25 and ≤ 50%	Caution	The path is tightening noticeably.	Investigate the cause and document.
> 50 and ≤ 75%	Warning	High risk of becoming critical.	Escalate; develop mitigation options.
> 75%	Critical watch	Buffers are functionally depleted.	Immediate action; treat as critical path.

By monitoring these thresholds, you can confidently interpret the schedule’s situation and take the necessary action to intercept slippage before it triggers a crisis on your critical path.

💡 Float erosion can be negative. If current float is greater than baseline float, the path has more breathing room than when the baseline was set. That’s not automatically good news. Float increases when upstream constraints are relaxed, logic is removed or a predecessor’s scope is reduced. Always investigate unexpected float increases to confirm they reflect genuine schedule improvement, not deleted logic.

Summary

By shifting the analytical focus from task slippage to active float erosion tracking, project controls teams transform basic variance reporting into an early warning system.

While measuring task slippage only tells you how far an activity has physically drifted from its plan, tracking float erosion evaluates the real consequence of that movement by calculating how much protective buffer remains.

Ultimately, this approach allows project managers to look beyond the immediate critical path, pinpoint which drifting activities pose the highest risk and deploy targeted interventions before performance slippage turns into a project delay.