Durations and duration types

A duration in Oracle Primavera P6 looks like a simple number of days, but P6 treats it as working time on a calendar, tracks it in four separate fields, and ties it to resource units through an equation. The duration type decides which part of that equation gives way when someone edits the schedule. Get it wrong in a resource-loaded file and a crew size, an hours budget or a finish date changes without anyone meaning to change it. This lesson explains durations and the four duration types, and what an owner should check in a contractor's baseline.

Learning outcomes

• Explain how P6 stores and displays durations, and the difference between Original, Remaining, Actual and At Completion durations.
• Use the equation Duration = Units ÷ Units/Time to predict what P6 recalculates when one value changes.
• Choose and set the four duration types at activity and project level in P6 Professional.
• Check a contractor's baseline for duration and duration-type problems before reviewing logic.

The lesson

A duration is working time on a calendar

When you type 5d into an activity's duration, P6 does not store "five days". It stores working time and counts it on the activity's calendar, which is why the same five days can finish on a Friday or the following Monday depending on holidays (see Lesson 5 on calendars). Oracle notes that P6 recalculates what you enter using the project calendar and the standard time periods your administrator has set, and that the available abbreviations are listed under Admin, Admin Preferences, on the Time Periods tab when you are connected to a P6 Professional database. On an EPPM database the same settings are in Application Settings [1]. If you want P6 to show the unit after each number, turn on Show Duration Label on the Time Units tab of User Preferences [1].

The practical point for owners: a duration only means something together with its calendar and the hours-per-day setting behind it. On Northgate, Monday to Friday at 8 hours a day, 1d is 8 hours of work.

Four duration fields, one activity

P6 keeps several durations for every activity. You enter them on the Status tab of Activity Details (choose Project, Activities, select the activity, then Status), and which field you can edit depends on whether the activity has started [1]:

• Original (shown as Planned in some views) is the planned working time from planned start to planned finish [1][2].
• Actual is working time from the actual start to the actual finish, or to the data date while the activity is in progress [2].
• Remaining is working time from the remaining start to the remaining finish. Before the activity starts it equals the planned duration, and it is zero once the activity is complete [2].
• At Complete is working time from the current start to the current finish, so for a started activity it adds the time already spent to the time still to go [2].

Figure 1 shows the four fields on one in-progress activity. The distinction matters at every update. A contractor who changes the Original duration of a started activity to make it "fit" is rewriting the plan, not reporting progress. Remaining duration is the field that should move.

View the data

Field	Value	Measured from
Original	25d	Planned start to planned finish
Actual	10d	Actual start to data date
Remaining	18d	Data date to remaining finish
At Complete	28d	Actual start to remaining finish

The equation behind duration types

Once an activity has resources, P6 keeps three numbers in balance: Duration = Units ÷ Units/Time [3]. Units are the total hours of work (say 800 crew-hours). Units/Time is the rate (say 4 workers, or 32 hours a day). Change one and P6 must change another to keep the equation true. The duration type tells P6 which one to change [3]. Oracle's field description says the type should match the least flexible factor on the activity: the schedule, the work effort or the resource availability [4].

That is why the duration type only matters when resources are assigned. Oracle describes the field as controlling how remaining duration, units and units per time are calculated when you update an activity that has resources [4]. In an unloaded schedule, every type gives the same dates.

The four duration types

Oracle lists four types and says which kind of activity each usually suits [5]:

• Fixed Units/Time. The rate stays put. Use it where a fixed crew produces at a fixed rate; Oracle links it most often to Resource Dependent activities.
• Fixed Duration & Units/Time. The duration stays put and the remaining units change. Use it where the work must be done in a fixed period whatever resources are assigned; Oracle links it most often to Task Dependent activities.
• Fixed Units. Total work stays put, so adding resources shortens the duration; most often used with Resource Dependent activities.
• Fixed Duration & Units. Duration and total work both stay put, and the rate changes; most often used with Task Dependent activities.

Figure 2 summarizes what P6 recalculates for the three most common edits, based on Oracle's synchronization rules [3].

View the data

Duration type	Change units	Change duration	Change units/time
Fixed Units/Time	Duration	Units	Duration
Fixed Duration & Units/Time	Units/time	Units	Units
Fixed Units	Duration	Units/time	Duration
Fixed Duration & Units	Units/time	Units/time	Units

Setting the duration type

For one activity, choose Project, Activities, select the activity, open Activity Details, click the General tab and pick the Duration Type. The field is greyed out for Start and Finish Milestones, which have no duration [5]. For a whole project, choose Enterprise, Projects, open Project Details, click the Defaults tab and set the duration type under Defaults for New Activities. That default applies only to activities created afterwards; existing activities keep their type [6]. To change many activities at once, add the Duration Type column to the Activity Table and fill it down. In P6 EPPM the same field appears in the activity's General details on the Activities page.

Screenshot to come

Northgate worked example

Northgate Distribution Centre (fictional) is a 12,000 m² tilt-up warehouse in Vaughan, Ontario, built by Halvorsen Builders Ltd. (fictional) for Northgate Logistics Inc. (fictional) under a CCDC 2-2020 stipulated price contract (see the Northgate fact sheet). Halvorsen's baseline is imported as NDC-BL00 into the owner's NDC.SUB branch of the EPS. In Lesson 7 we checked its activity types. Now the owner's scheduler checks durations.

The slab, resource-loaded

Activity A3500, Slab-on-grade (WBS 3.2), is Task Dependent with an Original duration of 25d, from Mon Apr 12 to Fri May 14, 2027, ending at the M4 milestone. For this example, assume Halvorsen has loaded it with a concrete finishing crew of 4 workers, 8 hours a day: 4 × 8 × 25 = 800 hours (illustrative numbers). The activity is in balance: 800 h ÷ 32 h/d = 25d.

Halvorsen's site superintendent wants to show the slab done in 20 days. What happens to the hours and the crew depends on the duration type (Figure 3):

• Fixed Units/Time or Fixed Duration & Units/Time: P6 keeps the crew at 4 and cuts the hours to 640. The schedule now claims the same slab can be placed and finished with 160 fewer hours of work. Nothing about the scope changed.
• Fixed Units or Fixed Duration & Units: P6 keeps the 800 hours and raises the rate to 40 h/d, which is 5 workers. That is at least a statement Halvorsen can be asked to stand behind: a bigger crew.

View the data

Case	Duration	Units (h)	Units/time	Crew
Before	25d	800	32 h/d	4
Fixed Units/Time	20d	640	32 h/d	4
Fixed Duration & Units/Time	20d	640	32 h/d	4
Fixed Units	20d	800	40 h/d	5
Fixed Duration & Units	20d	800	40 h/d	5

The opposite edit

Now suppose a change in slab thickness adds work and the estimator raises the units from 800 to 1,000 hours. Under Fixed Units/Time or Fixed Units, P6 lengthens the duration: 1,000 ÷ 32 = 31.25 days, so the slab and everything driven by it moves out, including M4. Under either of the two Fixed Duration types, the duration stays at 25d and the crew rate goes up instead [3]. Neither is wrong. What the owner needs to know is which one the contractor chose, so that a cost change and a time change are not quietly traded for each other.

The review

The owner's scheduler adds the columns Duration Type, Original Duration, Remaining Duration and At Completion Duration to the Activities window, groups by Duration Type, and checks:

• One deliberate default. Most construction tasks in one type, recorded from the Project Details Defaults tab.
• Exceptions with reasons. Any Fixed Units or Fixed Units/Time activity should be resource-loaded and Resource Dependent or otherwise explained.
• Durations within the specification. The Northgate schedule specification asks that construction activities not exceed 20 working days unless the owner accepts a reason. A slab at 25d is an obvious candidate for splitting into pours. P6's Check Schedule report includes a Large Durations check for exactly this [7].
• Original equals At Completion at baseline. In a baseline with no progress, the two should match. If they don't, something has already been statused.

Screenshot to come

Screenshot to come

Owner's move

• Name the default duration type in the specification. For an unloaded or lightly loaded schedule, a Fixed Duration type keeps dates stable when hours are edited. Whatever you choose, ask for it in writing and check the Defaults tab.
• Ask for durations in working days. Hours or weeks invite rounding errors and confuse the hours-per-day conversion.
• Set a maximum duration. Long activities hide progress. A 20-working-day limit for construction work, with exceptions for procurement and Level of Effort, is a common, workable rule.
• Watch Original durations on started work. In updates, compare Original Duration against the baseline. A change there is a re-plan and needs an explanation, not a progress entry.

Common mistakes

1. Changing the project default and expecting existing activities to follow. The Defaults tab affects new activities only [6].
2. Squeezing a duration on Fixed Units/Time. The work hours shrink to fit, and the schedule now understates effort.
3. Editing Original duration to report progress. Status goes in Actual and Remaining; Original is the plan.
4. Ignoring the calendar behind "d". A day is whatever the hours-per-period setting says. Mixed 8-hour and 10-hour calendars make day counts misleading.
5. Mixing duration types for no reason. Two identical pours with different types will react differently to the same edit.

Quick quiz

1. The equation P6 keeps in balance for a resourced activity is:

   1. Units = Duration ÷ Units/Time
   2. Duration = Units ÷ Units/Time
   3. Duration = Units × Units/Time
   4. Units/Time = Duration × Units

2. On a Fixed Units/Time activity, you shorten the duration. P6 recalculates:

   1. Units
   2. Units/Time
   3. The calendar
   4. Nothing

3. You change the project's default duration type on the Defaults tab. Existing activities:

   1. Switch to the new type
   2. Switch only if not started
   3. Keep their current type
   4. Lose their resource assignments

4. For an activity that has started, the duration that should change when the contractor reports progress is:

   1. Original
   2. Remaining
   3. Planned
   4. Baseline

5. Northgate's slab has 800 hours of work. Under Fixed Units, the duration is cut from 25d to 20d. The crew rate:

   1. Stays at 32 h/d
   2. Rises to 40 h/d
   3. Falls to 25.6 h/d
   4. Cannot change

Show answers and explanations

1. B. Oracle states the relationship as Duration = Units ÷ Units/Time [3].
2. A. Fixed Units/Time holds the rate, so a duration change recalculates units [3].
3. C. The default applies only to new activities [6].
4. B. Remaining duration covers the work still to do; Original is the plan [1][2].
5. B. Fixed Units holds the 800 hours, so the rate becomes 800 ÷ 20 = 40 h/d, five workers [3].

Key terms

Original duration

The planned working time from planned start to planned finish.

Remaining duration

Working time left from the remaining start to the remaining finish; zero when complete.

At Complete duration

Actual plus remaining working time; the current forecast of the activity's total length.

Units

The total amount of work on an assignment, usually in hours.

Units/Time

The rate at which a resource works on an assignment, such as 32 hours a day or 4 workers.

Duration type

The setting that decides whether P6 recalculates duration, units or units/time when one of them changes.

References

1. Oracle. Enter activity durations. Primavera P6 Professional Help, Version 26.
2. Oracle. Durations Columns of the Activity Table. Primavera P6 EPPM Help, Version 26.
3. Oracle. Synchronizing activity duration, units, and resource units/time. Primavera P6 Professional Help, Version 26.
4. Oracle. General Columns of the Activity Table. Primavera P6 EPPM Help, Version 26.
5. Oracle. Define activity duration types. Primavera P6 Professional Help, Version 26.
6. Oracle. Set the project default activity duration type. Primavera P6 Professional Help, Version 26.
7. Oracle. Dates and Durations tab - Check Schedule dialog box. Primavera P6 Professional Help, Version 26.

Verified on November 6, 2026.

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