Activity types: Task, LOE, WBS summary, milestones

Every activity in Oracle Primavera P6 has an activity type, and the type decides how P6 works out the activity's dates. Two activities with the same duration and the same links can finish on different days because one is Task Dependent and the other Resource Dependent. A supervision bar can stretch or shrink without anyone touching it because it is Level of Effort. For an owner reviewing a contractor's file, the activity type column is one of the fastest ways to find a schedule that looks right but will not behave.

Learning outcomes

• Name the six P6 activity types and explain how each one gets its dates.
• Set an activity's type in P6 Professional and group a schedule by type.
• Choose the right type for construction work, ongoing support work, summaries and contract milestones.
• Check a contractor's baseline for activity-type errors before reviewing its logic.

The lesson

Six types, one rule

P6 Professional has six activity types: Task Dependent, Resource Dependent, Level of Effort, Start Milestone, Finish Milestone and WBS Summary. Oracle states that types control how an activity's duration and dates are calculated, and that every activity must have one [1]. You set it in the Activities window: choose Project, Activities, select the activity, open Activity Details, click the General tab and pick the Activity Type [2].

The six types split into two families. Four have their own duration or logic position: Task Dependent, Resource Dependent and the two milestones. Two take their dates from other activities: Level of Effort and WBS Summary. Figure 1 shows the split.

Task Dependent: the default for construction work

On a Task Dependent activity, every assigned resource is scheduled on the activity's calendar, not on its own resource calendar [3]. Oracle suggests it where several resources on one activity have to work together [3]. That describes most site work: a formwork crew, a pump and a finisher pour a slab as one operation. Most activities in a contractor's construction schedule should be this type, and many contractors never use anything else for real work.

Resource Dependent: when resources keep their own hours

On a Resource Dependent activity, each resource is scheduled on its own calendar, so the activity's duration depends on when its resources are available [4]. Oracle suggests it where several resources on one activity can work independently [4]. Figure 3 in the worked example shows the effect: same work, same resources, a later finish.

Use it deliberately. It only behaves predictably when the schedule is resource-loaded and the resource calendars are maintained. In a schedule with no resources, the type adds nothing; in a schedule with stale resource calendars, it moves dates for reasons nobody can see in the Gantt chart.

Level of Effort: support work that follows the job

A Level of Effort (LOE) activity has no duration of its own. Its span runs from the earliest early start of the activities linked to its start to the latest early finish of the activities linked to its finish [5]. You cannot put constraints on it, resource levelling skips it, and it summarizes its dates using its own calendar [5]. Oracle's examples are clerical work, a security guard and some project management tasks [5]; the P6 EPPM help adds that administrative work is typically coded this way [11].

The usual build is an SS link from the activity that starts the support period and an FF link from the activity that ends it. LOE activities may take any relationship type [5]. Oracle compares them with hammock activities, which accept only SS and FF links and are not scheduled on their own calendar [5]. The practical rule for owners is simple: an LOE should follow the work, never lead it. If an LOE has a driving successor, something real is waiting on a bar whose length nobody estimated.

WBS Summary: a bar for a branch

A WBS Summary activity rolls up a WBS element. Its start is the earliest start of the activities in its group and its finish is the latest finish, and the group covers its own WBS code and every level below it. A summary on element 3 covers 3.1, 3.2 and anything beneath them; a summary on 3.1 covers only that branch [6]. Its duration is counted on its own calendar, it cannot take constraints, and any relationships you attach to it are ignored during scheduling and levelling [6]. You also cannot assign resources that drive activity dates to it [2].

That last point catches people. A scheduler who links the next trade to a WBS Summary thinks the logic is there. P6 ignores it, and the successor floats free. The WBS structure from Lesson 6 decides what each summary covers, so a clean WBS comes first.

Start and Finish Milestones

A Start Milestone marks the beginning of a major stage and a Finish Milestone marks the end [7][8]. Both have zero duration. They may have a primary resource and expenses, but not resource or role assignments or time-based costs such as labour, and you can attach work products and documents [7][8]. When you link to a milestone, P6 proposes Finish to Start by default [7][8]. To create one, set the Activity Type on the General tab to Start Milestone or Finish Milestone [9].

In practice, a Start Milestone carries only a start date and a Finish Milestone only a finish date, so the choice is not cosmetic. "Site mobilization" is a start. "Roof complete" is a finish. Pick the type that matches the event the contract names.

Screenshot to come

Northgate worked example

Northgate Distribution Centre (fictional) is a 12,000 m² tilt-up warehouse in Vaughan, Ontario, built under a CCDC 2-2020 stipulated price contract by Halvorsen Builders Ltd. (fictional) for Northgate Logistics Inc. (fictional). Halvorsen's baseline, due Wed Feb 10, 2027, arrives as an XER and is imported as NDC-BL00 into the owner's NDC.SUB branch. The owner's scheduler reviews activity types before looking at logic or float (see the Northgate fact sheet).

What the specification asks for

Northgate's schedule specification says the contract milestones that fall in Halvorsen's scope must appear as milestone activities with the owner's milestone number in the name. M3 (site mobilization, Mon Mar 1, 2027) and M8 (commissioning starts, Mon Nov 1, 2027) are Start Milestones. M4 to M7, M9 (Ready-for-Takeover / Substantial Performance, Fri Jan 14, 2028) and M11 (final completion, Fri Mar 31, 2028) are Finish Milestones. M10, the start of the owner's separate racking contract on Mon Jan 17, 2028, stays in the owner's Microsoft Project master. Support work such as site supervision and testing may be LOE; WBS Summary activities are allowed but may not carry logic.

One stage, five types

Figure 2 shows how the types work together in WBS 3, foundations and slab-on-grade. The foundations work itself is Task Dependent. A Level of Effort for quality control and testing is tied to it: SS from the start of footings and FF from the end of the slab, so it stretches if the slab runs late. The WBS Summary for element 3 spans the same work without any links of its own. The stage opens after the M3 Start Milestone and closes with the M4 Finish Milestone.

View the data

Activity	Type	Start	Finish	Dates set by
M3 Site mobilization	Start Milestone	Mon Mar 1, 2027	None	Logic (contract milestone)
WBS 3 summary	WBS Summary	Mon Mar 15, 2027	Fri May 14, 2027	Earliest start, latest finish in WBS 3
3.1 Footings & piers	Task Dependent	Mon Mar 15, 2027	Fri Apr 9, 2027	Duration and logic
3.2 Slab-on-grade	Task Dependent	Mon Apr 12, 2027	Fri May 14, 2027	Duration and logic
QC & testing, foundations	Level of Effort	Mon Mar 15, 2027	Fri May 14, 2027	SS from 3.1, FF from 3.2
M4 Foundations & slab complete	Finish Milestone	None	Fri May 14, 2027	Logic (contract milestone)

Task or Resource Dependent?

Halvorsen's fire alarm verification in WBS 7 needs an electrical crew and a fire alarm technician, each for three days. Suppose the technician's resource calendar shows Monday, Wednesday and Friday only. As Task Dependent, both resources follow the activity's Monday-to-Friday calendar and the activity finishes Wednesday; the technician's real availability is ignored. As Resource Dependent, the technician works Monday, Wednesday and Friday, so the activity finishes Friday (Figure 3). Neither answer is wrong. The question for the owner is whether the type matches how the work will really be done, and whether the resource calendars behind it are maintained.

View the data

Case	Electricians work	FA technician works	Activity span
Task Dependent	Mon, Tue, Wed	Mon, Tue, Wed (activity calendar)	Mon to Wed
Resource Dependent	Mon, Tue, Wed	Mon, Wed, Fri (own calendar)	Mon to Fri

The review

The owner's scheduler opens NDC-BL00 read-only, chooses View, Group and Sort By and groups by Activity Type [10]. Six bands, one per type, make the checks quick:

• Milestone bands. M3 and M8 under Start Milestone; the others under Finish Milestone; every in-scope M-number present once.
• Task Dependent band. No zero-duration tasks pretending to be milestones.
• Resource Dependent band. Each one resource-loaded, with a reason.
• Level of Effort band. Support work only, and no LOE driving a successor.
• WBS Summary band. No relationships attached, since P6 ignores them.

Screenshot to come

Owner's move

• Specify milestone types, not just milestone dates. Name which contract milestones are starts and which are finishes, and require the owner's milestone numbers in the activity names so they survive every update.
• Limit LOE to support work. Supervision, site services and testing support are fine. Anything with a real crew and a real quantity is not.
• Ban logic on WBS Summary activities. They are reporting bars. Logic attached to them is ignored [6] and gives a false sense that the schedule is linked.
• Ask why for every Resource Dependent activity. If the contractor cannot point to the resource calendar that justifies it, ask for Task Dependent.
• Check types before logic. A type error changes dates, so a logic or float review on a file with type errors is wasted effort. Our schedule review guide covers what to check next.

Common mistakes

1. Coding real work as LOE. Concrete curing or panel erection as LOE has no estimated duration, so it can never be late on paper.
2. Linking successors to a WBS Summary. P6 ignores the link, the successor loses its driver, and float looks better than it is.
3. Using the wrong milestone type. A Finish Milestone for "mobilization starts" reports the wrong date field and confuses every report built on it.
4. Zero-duration Task Dependent activities. Use a milestone type instead; it says what the activity is and stops resources being loaded onto it.
5. Switching to Resource Dependent without resource calendars. The type then behaves unpredictably as calendars change, and dates move with no visible cause.

Quick quiz

1. On a Task Dependent activity, resources are scheduled using:

   1. Each resource's own calendar
   2. The activity's calendar
   3. The global calendar only
   4. The project's default calendar only

2. The span of a Level of Effort activity is set by:

   1. Its original duration
   2. A primary constraint
   3. The activities linked to its start and finish
   4. Resource levelling

3. A successor is linked to a WBS Summary activity. During scheduling, P6:

   1. Drives the successor from the summary's finish
   2. Ignores the relationship
   3. Converts the summary to a Finish Milestone
   4. Reports a scheduling error and stops

4. Which can a Finish Milestone have?

   1. A labour resource assignment
   2. A five-day duration
   3. Expenses and a primary resource
   4. Time-based costs

5. Northgate's M3 site mobilization should be entered as:

   1. A Start Milestone
   2. A Finish Milestone
   3. A Level of Effort
   4. A WBS Summary

Show answers and explanations

1. B. Task Dependent activities schedule their resources on the activity's calendar [3].
2. C. An LOE runs from the earliest early start of activities linked to its start to the latest early finish of those linked to its finish [5].
3. B. Relationships assigned to WBS Summary activities are ignored during scheduling and levelling [6].
4. C. Milestones can have expenses and a primary resource, but no resource assignments, durations or time-based costs [8].
5. A. Mobilization marks the start of a stage, which is what a Start Milestone represents [7].

Key terms

Activity type

The setting that controls how P6 calculates an activity's duration and dates. Every activity has one.

Task Dependent

Resources are scheduled on the activity's calendar.

Resource Dependent

Each resource is scheduled on its own calendar, so availability can change the duration.

Level of Effort (LOE)

An ongoing support activity whose span is set by the activities linked to it.

WBS Summary

An activity that spans the earliest start to latest finish of the activities in its WBS element and below.

Start Milestone / Finish Milestone

Zero-duration activities marking the start or end of a major stage.

Hammock

A summary-style activity that accepts only SS and FF links. Oracle compares it with P6's LOE, which is similar but not the same.

References

1. Oracle. Activity types. Primavera P6 Professional Help, Version 26.
2. Oracle. Define activity types. Primavera P6 Professional Help, Version 26.
3. Oracle. Task dependent activity. Primavera P6 Professional Help, Version 26.
4. Oracle. Resource dependent activity. Primavera P6 Professional Help, Version 26.
5. Oracle. Level of effort activity. Primavera P6 Professional Help, Version 26.
6. Oracle. WBS summary activity. Primavera P6 Professional Help, Version 26.
7. Oracle. Start milestone activity. Primavera P6 Professional Help, Version 26.
8. Oracle. Finish milestone activity. Primavera P6 Professional Help, Version 26.
9. Oracle. Define milestones. Primavera P6 Professional Help, Version 26.
10. Oracle. Group activities by field. Primavera P6 Professional Help, Version 26.
11. Oracle. About Activity Types. Primavera P6 EPPM Help, Version 25.

Verified on November 4, 2026.

Next lesson in this trackDurations and duration types