Today we’re examining date and duration variances in P6.
When your P6 Professional date or duration variance field is positive or negative, is that a good or bad sign? Let’s take a look.
A P6 Professional baseline is like a static ruler used to measure distances. The baseline is a static picture of the schedule in time, marking the original start and finish dates to measure variances from these dates when the schedule progresses. The fundamentals of P6 baselines are discussed in the following article:
Once you’ve assigned a baseline, P6 has a set of variance fields that compare the live schedule against it. When P6 presents positive variance results, the question becomes whether that is good news or bad. You want to quickly interpret the positive/negative variance outcomes to make a speedy, accurate assessment of your schedule.
In this article, we look at how to interpret the date and duration variances to effectively understand and report on these variance fields in P6 Professional.
The Golden Rule: Positive vs. Negative Variance
When interpreting variance results, the following general guidelines are helpful.
| Variance Sign | What It Means for Date Fields |
| Positive (+) | The live date is EARLIER than the baseline date (ahead of schedule) |
| Negative (−) | The live date is LATER than the baseline date (behind schedule) |
P6 calculates variance so that a positive variance always represents a favorable outcome. This agrees with intuition. A positive Start Variance means the activity is starting earlier than planned, which is good.
A negative Finish Variance means it finishes later than planned, which is bad. P6 calculates variance as Baseline minus Live, so later dates produce negative numbers.
| ⚠️ ‘Positive variance’ means ‘good performance.’ In P6 variance fields, positive = ahead, negative = behind. This agrees with how many people intuitively read the word ‘positive’. But make sure your stakeholders understand the convention. |
Before proceeding, note how Primavera P6 identifies baselines:
- BL Project: The Master Project Baseline.
- BL1: The Primary User Baseline.
- BL2: The Secondary User Baseline.
- BL3: The Tertiary User Baseline.
In this article, the variance equations are based strictly on the BL Project. While schedulers are typically free to modify the user baselines (BL1–BL3) for ad-hoc analysis, the BL Project baseline is often controlled by a System Administrator to maintain an official performance record.
Variance – BL Project Start Date (Start Date Variance)
Formula: Variance – BL Project Start Date = BL Project Start – Start
This tells you how far the activity’s current planned start has shifted from the baseline project start. A positive number means the activity is planned to start earlier than originally scheduled. A negative number means it’s planned to start later.
| Scenario | BL Project Start | Current Start Date | Variance – BL Project Start Date | Reading |
| Started on time | Day 10 | Day 10 | 0 | No slippage |
| Starting early | Day 10 | Day 5 | +5 days | 5 days ahead of plan |
| Starting late | Day 10 | Day 13 | −3 days | 3 days behind plan |
For activities that have already started, P6 compares the BL Project Start date against the Actual Start date. For activities not yet started, it compares against the Early Start Date. This means Start Variance locks in once an activity begins.
Variance – BL Project Finish Date (Finish Date Variance)
Formula: Variance – BL Project Finish Date = BL Project Finish – Finish
This is the most-watched variance field in scheduling. It tells you whether the activity is expected to be completed earlier or later than planned. For in-progress activities, it reflects the current projected finish (based on remaining duration from today) compared against the baseline project finish.
| Scenario | BL Project Finish | Current Finish Date | Variance – BL Project Finish Date | Reading |
| On track | Day 20 | Day 20 | 0 | No slippage |
| Ahead of plan | Day 20 | Day 12 | +8 days | 8 days ahead of plan |
| Running late | Day 20 | Day 23 | −3 days | 3 days behind plan |
| 💡 Finish Variance on completed activities Once an activity is complete, the Finish Variance = BL Project Finish − Actual Finish becomes a fixed historical fact. This value does not reset to zero upon completion; instead, it serves as a permanent record of how actual performance differed from the plan. |
Variance – BL Project Duration (Duration Variance)
Formula: Variance BL Project Duration = BL Project Duration – At Completion Duration
This compares the original baseline duration against the current total estimate (At Completion Duration).
- Positive Value: The activity takes less time than planned.
- Negative Value: The activity has been extended.
Note: Unlike other metrics, this variance uses the At Completion Duration (Actual + Remaining). For in-progress tasks, this means the variance reflects the total current scope required to finish, not just the original plan.
| Scenario | BL Project Duration | At Completion Duration | Variance | Reading |
| Efficient | Day 20 | Day 20 | 0 | No slippage |
| On Track | Day 20 | Day 12 | +8 days | 8 days ahead of plan |
| Running late | Day 20 | Day 23 | −3 days | 3 days behind plan |
| ⚠️ Variance – BL Project Duration ≠ Float Variance Duration Variance indicates changes in scope or effort, not necessarily schedule impact. Example: An activity could double in duration, but if it has enough Total Float, the project finish date remains unaffected.Best Practice: Always evaluate Duration Variance alongside Finish Variance and Total Float to understand the true impact on your deliverables. |
Reading Variance Fields Together: A Worked Example
An activity in isolation can tell a misleading story. Here’s how to read variance fields together:
| Field | Value | What It’s Telling You |
| Variance – BL Project Start | +3 days | Started 3 days early |
| Variance – BL Project Finish | +3 days | Currently projected to finish 3 days early |
| Variance – BL Project Duration | 0 | Duration hasn’t changed — schedule starts 3 days early and finishes 3 days early |
The picture here: the activity started early and is projected to finish early because the activity duration remains on plan.
Quick Reference: All Variance Fields
| Field | Formula* | Unit | What’s “Good”? |
| Variance – BL Project Start | BL Project Start – Start | Days | 0 or positive (On time/Started Early) |
| Variance – BL Project Finish | BL Project Finish – Finish | Days | 0 or positive (On time/Finished Early) |
| Variance – BL Project Duration | BL Project Duration – At Completion Duration | Days | 0 or positive (On time/Shorter duration |
*Note: For in-progress or completed tasks, the “Start” and “Finish” dates in these formulas refer to the Actual dates.
Summary
Before analyzing date or duration variances, ensure the schedule was baselined prior to status updates and that the baseline is assigned to a specific slot. P6 categorizes variance columns to match these assignments:
- Project Baseline: Uses columns labeled BL Project (e.g., Variance – BL Project Finish).
- User Baselines: Uses columns labeled BL1, BL2, or BL3 (e.g., Variance – BL1 Finish).
P6 equations align with your intuition, where a positive result is a favorable outcome. The Variance – BL Project Finish Date is the most vital metric; it tells you if an activity, a key deliverable or the entire project is expected to finish earlier or later than planned.”
Meanwhile, Variance – BL Project Duration compares the baseline against the At Completion Duration (Actual + Remaining) to show if the total work time has changed.
Reading these variances together provides a panoramic view, helping you determine whether a finish delay is due to a late start, a slower work pace or a change in scope.