As a Primavera P6 Professional and Oracle Primavera Cloud trainer, I often assist users with project issues. One common question I receive relates to schedule drift. This is where an activity’s data changes unexpectedly after scheduling. Most commonly, you’ll see this during status updates. While scheduling the project, activity’s finish date or duration may change without prompt.

In Primavera programs, this often occurs due to improper scheduling techniques. If not resolved, this can lead to significant project delays and increased durations.

There is a simple solution to this problem, and it comes from understanding how the Primavera scheduler works. In this article, we will take a look why schedule drift can occur and what to do to prevent it.

The following examples are taken from Primavera P6 Professional. The scheduling principles discussed will also apply to other Primavera schedule management programs, including Oracle Primavera Cloud and Primavera P6 EPPM.

The Problem: Schedule Drift and Increased Durations

The root cause of this issue lies in users trying to schedule in P6 the way that they would in Microsoft Project. These programs function quite differently – especially in regards to the schedule tool. It is recommended that users transitioning to P6 undergo training to fully understand how the program operates. Knowledge of MS Project alone is insufficient for scheduling in Primavera P6.

When using the Schedule tool in P6, the program will use the Critical Path Method algorithm to calculate planned dates for each activity. This calculation will look at activity durations and relationships to determine ideal dates. The Schedule tool will ensure that all activities can be completed within the set time frame. Once the project starts, the user will need to update the activities with actual data – such as the Actual Start and Actual Finish dates. By comparing these actuals with the planned dates, you can assess whether the project is ahead, behind, or on schedule.

Schedule drift can occur when users improperly perform status updates. Let’s take a look at an example. Below, I have an activity called Rough Grade. This activity has 10 days of duration and a planned start date of January 25th.

Hold shift key to keep line markup tools straight in Bluebeam Revu 2019

Suppose it is now February 1st, and I’m performing my first status update. Rough Grade started on January 25th as planned, but it is still in progress at this moment. Former MS Project users may stop here, assuming that updating the Actual Start is enough to progress the activity. However, this is the cause of the schedule drift issue.

Currently, Rough Grade is set to finish on February 7th (10 days after the start). Let’s see what happens when I schedule the project and move the Data Date. To do this, select Tools > Schedule. In the Schedule window, I can move the Data Date, which represents the up-to date for the project. Shifting the Data Date recalculates activities based on the work completed thus far. While this feature can be very useful, incorrect usage can lead to major schedule issues.

Let’s observe the changes to Rough Grade after moving the Data Date. I’ll move the Data Date to February 1st, the date the status update is being performed.

After scheduling the project, Rough Grade‘s planned finish date has changed. It is now planned to finish on February 14th, with an At Complete duration of 15 days – up from the original 10 days. Additionally, the project finish date has moved from September 25th to October 3rd.

This has drastically changed my project. If this happens every time I schedule the project, I’ll have a myriad of schedule issues.

This outcome occurred because I didn’t use the scheduler properly. Let’s delve into how the P6 scheduler operates to understand this situation better. To revert the activities back to their original dates, I can schedule the project again and change the Data Date back to January 1st.

Understanding How the Primavera P6 Scheduler Works

Primavera P6 uses the Critical Path Method (CPM) algorithm to calculate activity dates based on dependencies, durations, and relationship types. When you update the project with actual data, such as Actual Starts and Actual Finishes, the scheduler will recalculate your activity dates and durations based on the work completed so far.

This is a very powerful tool, as if your activities are not going as planned, the program will calculate a new finish date for the project. You can then use this information to drive future project decisions as needed.

Along with the actual dates, the schedule tool considers the progress of ongoing activities. Based on the information you give the program, it will assess how much of the project is complete at any given time.

This is also where the Data Date comes into play. When you first create a project, the Data Date will be set to the project’s start date. The Data Date is the up-to date for the project, indicating how much the project wasm . As you continue to perform status updates, you will move the Data Date to match the update date. If any activities plan to be completed prior to the Data Date, but were not updated, the program will calculate new start and finish dates.

The Data Date allows you to reflect the progress of the project up to that date. However, improperly using of this feature can lead to schedule drift and incorrect activity durations.

How to Properly Update Activities

Now that we understand how the scheduler works, let’s look at how we can avoid schedule drift when performing status updates. There are two main reasons for schedule drift : improper use of the Data Date and not accounting for activity progress.

Using the Data Date

You should only move the Data Date after updating every activity within the update period. If I’m planning on moving my Data Date to February 1st, I need to make sure I’ve updated all progress for January.

In my project, I have a series of activities that have Planned Start dates in January – including Trench for Utility Lines, Lay Sewer Piping and so on.

If it is February 1st, and I’m performing a status update, I need to update all activities that have occurred prior to this date. If I don’t update these activities, the scheduler will assume that these activities were did not get done. The schedule tool will then push them to start/finish at a later date, increasing the duration of the project.

To show an example of this, I’ll mark off that Trench for Utility Lines has started and finished. However, I will not adjust any of the other activities set to take place in January. I’ll now schedule the project and move the Data Date forward to February 1st.

After scheduling the project, the completed activity, Trench for Utility Lines, did not move. Setting actual dates to an activity will lock it in place. However, all the activities that were supposed to start in January – but did not – were pushed forward by the Data Date. The program is assuming that these activities did not get done during January, but still need to be completed. Therefore, the program calculated a new start and finish date for those activities.

This is a powerful tool – if we didn’t get done with those activities, the program would tell us when they should be performed going forward. We can also see the effect of this delay on the project’s overall duration. But as you can see, if those activity dates were not supposed to change, I made a big error with my schedule.

If you are going to move the Data Date, you’re telling the program that you have updated all activities before that set date. Make sure you update all activities with progress before moving the Data Date.

Accounting for Activity Progress

For activities in progress, you MUST tell the program how much of the activity has been completed thus far. You can do this by updating the activity’s progress.

Let’s go back to our original example. On February 1st, I updated the activity of Rough Grade by entering in an Actual Start date of January 25th. However, I didn’t further update the progress of the activity.

If you don’t update the progress of an activity, the program will assume that the activity still needs its full duration for completion. Because I moved the data date forward to February 1st, the program assumed that 5 days of Rough Grade had been completed. But, because I hadn’t noted otherwise, it assumed that we still needed 10 days to complete the activity. Put simply, the activity’s planned duration was added to its duration up to the Data Date. This not only extended the activity’s finish date, but also increased the overall activity duration.

To avoid this, you need to tell the program how much of the activity has been completed at the time of the update. You can do this a couple ways:

Expected Finish

If you know when the activity will finish, you should enter in an Expected Finish date. If I wanted Rough Grade to finish on the planned date of February 7th, I would enter this date into the Expected Finish field.

% Complete

If you know how much of the activity has been completed thus far, you can enter in a % Complete value. If about 60% of Rough Grade has been finished, I would enter that into the Duration % field.

Remaining Duration

If you know how many days are remaining for the activity, you can enter in a Remaining Duration. If I knew that we had 4 days left for Rough Grade, I would enter 4 into the Remaining Duration field.

If you enter in any of these fields before scheduling the project and moving the data date, the activity’s finish date will NOT drift.

This time, after entering in the Actual Start date of January 24th, I’ll also update the activity’s progress. I’ll enter in an Expected Finish date of February 7th. With that completed, I will now schedule the project and move the data date forward to February 1st. Because I told the program when the activity would finish, the activity’s planned finish date did not change. Additionally, its At Complete duration stayed at 10 days.

Summary

Schedule drift in Primavera programs is almost always due to a misunderstanding of how the schedule tool works. In Primavera P6, Oracle Primavera Cloud, and Primavera P6 EPPM, you need to make sure that you provide as much information as possible about the updated activities. Not only will you need to enter in the activity’s actual starts and finishes, you will also need to report progress for in progress activities. Additionally, you’ll need to be aware of how the data date works. You should only ever move the data date once all activities prior to the update date have been statused.

When performing status updates in Primavera programs, you should follow this order of operations:

Gather all information from users on the field. Make sure you know when activities have started, have finished, and the progress of activities that are ongoing.Before performing a status update, make sure you have a saved baseline of the project’s current version.
Identify the activities that need to be updated within the schedule. You can do this with the use of a Lookahead Filter or the Progress Spotlight tool.
For each activity you’re updating, enter in an Actual Start date if the activity has started. If the activity has finished, enter in an Actual Finish date. If the activity is ongoing, enter in either an Expected Finish date, a Remaining Duration, or a % Complete value.
If the activities have resources, costs or units assigned to them, enter in those actual values, as well.
Once you have updated all activities within the update period, schedule the project by selecting Tools > Schedule. Move the Data Date to the date you have statused the project up to.
Once completed, create another baseline to save the project as it is.

If you follow these instructions for each update period, you will avoid common schedule issues like drift and delays.

If you have any comments, questions or suggestions, please use the comment section on the bottom of this page, and don’t forget to subscribe to our blog to get more Primavera P6 tips & tricks directly in your inbox!

Lauren Hecker is a Primavera P6 Professional and Oracle Primavera Cloud Instructor. She teaches onsite and virtual Primavera P6 and OPC training courses. To see her next open enrollment course, please visit our calendar. To schedule an onsite or custom course, please contact us!

← 10 Cool Buildings From Around the World Construction Robotics: Is the Industry Ready? →

Understanding and Preventing Schedule Drift in Primavera P6

The Problem: Schedule Drift and Increased Durations

Understanding How the Primavera P6 Scheduler Works

How to Properly Update Activities

Using the Data Date

Accounting for Activity Progress

Expected Finish

% Complete

Remaining Duration

Summary

0 Comments

Submit a Comment Cancel reply

Subscribe To Our Newsletter

You have Successfully Subscribed!