Level of Effort (LOE) activities in P6 are pretty handy and sometimes not used by less experienced schedulers. If you set them up properly, they can give you a dynamic summary bar that automatically stretches from the earliest start to the latest finish of whatever work you connect to it.
Once you know how P6 calculates LOE dates (and how they differ from WBS Summary bands), you’ll wonder how you ever worked without them!
In P6, a LOE is an activity with its type set to “LOE.” The key thing to know is that it doesn’t have its own duration. Instead, P6 works out its dates from whatever predecessors and successors you connect to it. The start comes from the earliest predecessor, the finish from the latest successor.
That makes it perfect for summarizing a chunk of work without creating a new Work Breakdown Structure (WBS) element. And because it updates automatically when the underlying activities move, there’s no manual LOE adjustment involved. Pretty cool, eh?
LOE Vs. WBS Summary Band
A WBS Summary band rolls up everything sitting under a WBS element, and it has no choice in the matter.
A LOE, on the other hand, spans exactly what you tell it to. You wire it up with predecessor and successor relationships, which means it can reach across different WBS elements. It’s much more flexible.
How P6 Works Out the Dates
The math is easy:
ES (LOE) = Earliest Start among all predecessors EF (LOE) = Latest Finish among all successors Duration = EF − ES + 1 working day
Every time you choose Tools | Schedule > Schedule, or press Fn+F9 and click the Schedule button, P6 recalculates the duration to reflect the current span. You’ll see it update in the Original Duration column.
Forward pass: The LOE’s start is pushed by its predecessors, just like any other activity. If something upstream runs late, the LOE moves with it.
Backward pass: The LOE’s late finish is pulled by its successors. P6 works back through it the same way it does for any activity with a duration.
Float on a LOE LOEs can show total float just like regular activities. Because the LOE spans a whole block of work, its float value reflects the widest span. So, zero float on a LOE means that the entire phase is on the critical path. This can be handy for phase-level reporting.
How to Set One Up
Our demonstration schedule is below, showing the Activity table, Gantt chart and an LOE project management task. We want to add Safety Management LOE to span the construction work duration.
Step 1 — Create the activity: Add a new activity below Project Management and set the Activity Type to LOE. Leave the duration blank; P6 will fill it in.
Step 2 — Add predecessors: Link the first activity in the group or phase to the LOE (FS or SS). This drives the LOE’s start date.
Step 3 — Add successors: Link the LOE to the last activity in the group or phase (FS or FF). This drives the LOE’s finish date.
Step 4 — Schedule Fn+F9 and click the Schedule button. The start, finish and duration all get calculated automatically.
Watch Out: Don’t link a LOE back to itself. If an activity is both a predecessor and a successor of the same LOE, you’ve got a circular loop and P6 will throw an error. Keep your predecessors and successors pointing in the same direction.
LOE vs WBS Summary
| Feature | LOE Activity | WBS Summary Band |
| Date source | Driven by its predecessor/successor links | Automatically spans everything in the WBS element |
| Cross-WBS spanning | Yes — works across any WBS elements | No — only covers its own WBS element and children |
| Where it sits | Anywhere in the network; shows as a Gantt bar | Fixed to the WBS hierarchy; not schedulable |
| Float | Calculated independently | Earliest/latest roll-up; no independent float |
| Reporting | Shows in Activity Table and Gantt; fully filterable | Only visible when WBS grouping is on; not filterable |
| Best for | Cross-functional phase or work package summaries | Summarizing all work under one WBS element |
Where LOEs Actually Come in Handy
Phase duration reporting — Throw a LOE across all activities in a construction phase, and you’ve got a single bar that shows when the phase starts and ends. It updates itself as the schedule shifts. No manual fiddling.
Contract milestone spans — Use an LOE to represent a contractual stage, like “Detailed Design,” pulling in all relevant design activities regardless of their WBS. The bar tells you the contractual stage duration straight away. This is useful for invoicing and reporting.
Interface management — Got multiple projects in P6? An LOE in Project A can link to milestones in Project B. This gives the interface manager one bar that shows the entire external dependency window between the two.
Quick Checklist
- Set Activity Type to LOE. Don’t assign a manual duration.
- Link up predecessors to the first activities in the span (FS or SS into the LOE).
- Link up successors to the last activities in the span (FS or FF out of the LOE).
- After scheduling, check that the start and finish times look correct. If not, you’re probably missing a relationship.
- Don’t create circular logic by linking a LOE back to its own predecessors.
- Use LOEs for cross-WBS spans and use WBS Summary bands when everything’s under the same WBS element.
- Check LOE float after leveling. It tells you the aggregate float for the whole block.