When working on a project in Primavera P6, there are a lot of variables you’ll need to track and manage – such as lags and constraints. Typically, the usage of these variables will depend on your contract. While one contract may allow you to use constraints and lags, another contract may forbid it. In Primavera P6, relationship lag can be especially difficult to identify – especially in a larger project schedule. There is no Lag column that you can add to the activity table. This makes it difficult to determine which activities have lag values and which do not. However, there are a few ways to identify lag in Primavera P6 – such as creating reports and using the Check Schedule Report tool. 

In this article, we will cover a variety of different ways to identify relationship lag in Primavera P6 Professional. First, we’ll look at how to use the Predecessor Details and the Successor Details columns to display lag within the table. Next, we’ll go over how to create a report to quickly identify a list of activities with lag. Lastly, we’ll look at how to use the Check Schedule Report to get a full list of activities with lag. The following examples are all from Primavera P6 Professional 24 – but most of these tools are available in all versions of P6.

What is Relationship Lag?

Relationship lag, or lag, is a waiting period between two activities in a relationship. The lag value is the number of days between the finish of the predecessor activity and the start of the successor. Even with Finish to Start relationships, you can’t always go immediately from one activity to another. For example, you might have limited resources available, or need to account for curing time. In these cases, you can use lag to add a break period between the two linked activities. P6 allows you to use both positive and negative lag.

Positive Lag

Positive lag, as mentioned earlier, is a waiting period between the two activities. The successor will not be able to begin until both the predecessor and the lag value have finished.

Most project schedules allow the use of positive lag – but you should not overuse it. It’s a best practice to use lag on less than 5% of all activities in the schedule. This lag value should generally be a short duration – ideally, it should not exceed 14 days. As you’ll see shortly, it is hard to identify lag on the schedule. Lag is not easily apparent when looking at the Gantt Chart or activity dates. It’s generally a better practice to use an activity to represent the lag time instead. This will make the waiting period much more obviously apparent on both the table and the Gantt Chart. Additionally, everyone will now know exactly what the waiting period is for.

In the example above, I have two activities, Pour Footings and Strip Footings, tied together in a FS relationship. Because these activities involve concrete, we need to account for the curing time. We could do this with lag between the two activities. However, instead of using lag, I could add an activity between them called Footing Cure Time. Now, it’s very clear what this waiting period is for.

Negative Lag (Lead)

Negative lag, otherwise known as Lead, will overlap two activities in a relationship. This allows the successor activity to start before the predecessor activity finishes. Negative Lag is the direct opposite of positive lag. Rather than waiting extra time for the successor to start, the successor will start earlier than the predecessor’s finish.

Negative lag is typically seen as a bad scheduling practice. Most project contracts will prohibit the use of negative lag. Negative lag is harder to track and can cause issues with total float calculations. If possible, you should almost always avoid using negative lag.

Instead of using negative lag, you can achieve the same effect using positive lag and a SS or FF relationship. If two activities are set to start or finish on the same date and you give them lag, you can get the same overlapping effect as negative lag. This is always an option to use if you need to overlap tasks, but can not use negative lag.

Applying Lag to Relationships

You can apply lag to relationships in Primavera P6 using the Relationships tab in the Activity Details window. Under both the Predecessor and the Successor side, you’ll find a column for Lag. You can enter either a positive or negative number to enter in the desired lag value.

You will see the effect of the added lag value after using the Schedule tool.

Unfortunately, there is no Lag column that you can add to the activity table. To view relationship lag, you will have to use the Relationships tab in the Details section. However, there are a few ways you can set up the program to better identify lag. You can either use the Predecessor/Successor Details columns, set up a report, or use the Check Schedule Report tool.

Viewing Lag in Activity Columns

Although there is no Lag column, there are columns that you can add to the Activities table that will display lag values. Since the release of Primavera P6 Version 16, there are now columns for Predecessor Details and Successor Details. To add these columns to the table, select View > Columns. You can find these columns under the Lists category and add them to the table by double clicking on them.

These columns will display the IDs of the selected activity’s predecessors and successors – along with any added lag value. You’ll either see a positive number for positive lag, or a negative number for negative lag. This can be useful for identifying lag values for each activity. However, you will have to scan through each activity manually.

Even with these columns displaying, it is not easy to filter for activities with lag. Even if you create a filter for either Predecessor Details or Successor Details, the best you can do is filter for activities that contain a number within these cells. However, most Activity IDs also include numbers – so this will not only show you activities with lag. Luckily, there are a few other ways to quickly identify activities with lag.

Creating a Relationship Lag Report

Although there is no option to filter for lag on the Activities screen, this is an option within the Reports screen. Using this filter, you can create a report to quickly identify activities with relationship lag. In Primavera P6, reports are user-defined lists of data pulled from the database. Reports are useful for identifying specific types of activities – such cCritical activities or those with lag.

To create a report, navigate to the Reports page by selecting Tools > Reports > Reports. Here, you’ll find a variety of default reports – but you can also create a new custom report by selecting Edit > Add.

Configuring the Report

The Report Wizard will open to walk you through the process of creating a new report. First, you’ll need to select a Subject Area to focus the report on. Because lag applies to Activity Relationships, select this as the main subject area. Then, press Next. You have the option to add additional subject areas as well – but in this case, you can leave this blank and select Next.

Under Configure Selected Subject Areas, you can choose what information will display within the report. First, adjust the report’s columns by selecting Columns. It’s up to you which columns to display, but I recommend adding the following columns to track relationship lag:

• Predecessor ID
• Predecessor Name
• Relationship Type
• Lag
• Successor ID
• Successor Name

These columns will show you all needed information about both the activity’s relationships and its lag values.

You can choose to Group and Sort your activities here – such as by WBS or Project – but I’ll leave this as it is. We will likely not have a long list of activities with lag, and grouping and sorting may overcomplicate the report.

Lastly, select Filter to define a filter. If you do not add a filter to the report, the report will give you information about every activity in the schedule. For this report, we only want to see information for activities with lag, and we can do this by creating a filter. Here, use the dropdown fields to set the filter to Where – Lag – is not equal to – 0d. This will allow us to only see activities with a lag value displaying. Then, press OK.

Running the Report

Give your report a Title, and then select Run Report. You can choose a format to save the report as, and once run, it will automatically open. Now, we have a quick list of all activities with lag within the open project.

Press Next, and the final screen will let you Save the report. It’s a good idea to save this report, as this will allow you to run the report on other projects in the future. Your report will automatically appear in the Reports list. Now, you can run this report on any open project by right clicking on it and selecting Run > Report. Although reports take some initial setup, we now have a relationship lag report that we can use at any time, on any project.

Using the Check Schedule Report Tool

With the release of Primavera P6 Version 22, there is now another tool that can help you identify relationship Lag: Check Schedule Report. This is a pre-built report that will analyze your project’s health and identify potential problem areas. Additionally, it also provides a list of activities with both positive and negative relationship lag.

To use this tool, select Tools > Check Schedule Report. A window will open, showing all the metrics that the report will track within your schedule. You can use the checkboxes to turn any of these metrics on or off. If you just wanted to identify lag values, you could deselect all values except Negative lags and Positive lags.

With your parameters set, select Check Schedule. An HTML file will automatically open, showing the results of the report. At the top of the report, you will see the percentage of activities found for a specific check – such as the percentage of activities with lag. As you scroll down the report, you’ll see each individual activity listed, along with its lag value in hours.

With this report, you can quickly identify not only which activities have lag, but also the amount of lag they have.

Summary

In Primavera P6, relationship lag is a break or rest between two activities in a FS relationship. This is a common variable you’ll need to use when scheduling, as even with relationships, activities can’t always perform back to back. For example, if you’re working on activities involving concrete, you might need a break period to represent the curing time. The difficulty with using lag in Primavera P6 is that it’s not always easy to identify by just looking at the schedule. There is no Lag column you can add to the table, and you can not filter activities by whether they have lag. However, if you do need to identify lag, there are a few more manual ways to do this. You can use the Predecessor/Successor Details columns, create a report, or use the Check Schedule Report tool. With these tools, you can quickly identify which activities have lag and how that affects the overall project schedule.

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