Task types: units, duration, work

Once a task has a resource on it, Microsoft Project stops treating duration as a number you typed and starts treating it as one corner of a formula. Change the hours, the people or the days, and Project changes something else to keep the formula true. The task type decides what that something else is. Pick the wrong type and a review period quietly stretches, or half of a commissioning test disappears from the plan without a warning.

Learning outcomes

• Explain the Work = Duration × Units formula and what each term means in Project desktop.
• Predict what Project recalculates when you change units, duration or work under each task type.
• Set a task's type, show the Type column and change the default task type for new tasks.
• Choose a task type for common owner-side tasks: review periods, testing and staff time.

The lesson

One formula behind every assignment

Microsoft Project schedules resourced tasks with one relationship: Work = Duration × Units [1]. The three terms are easy to mix up, so it is worth being exact.

• Duration is the working time between a task's start and finish on its calendar, the number you learned to enter in Lesson 6. On Northgate's Monday-to-Friday, 8-hour calendar, 10 days is 80 working hours of elapsed working time.
• Work is effort: the person-hours a resource spends on the task. Two people for one day is 16 hours of work but only one day of duration.
• Units (assignment units) is the share of a resource's working time given to this task. 100% is one person full time; 50% is half their day; 300% can mean three people under one resource name [4].

So one commissioning agent at 100% for 10 days is 80 hours of work. The formula only bites once a resource is assigned. A task with no resources has a duration and no work, which is why many owner schedules never meet task types until someone starts loading resources (Lessons 16 and 17 cover the Resource Sheet and assignments).

Three task types, three things held still

A task type fixes one of the three values so that Project does not touch it when you edit the other two [1]. The Type field offers Fixed Units, Fixed Work and Fixed Duration, and Fixed Units is the default [2]. The setting applies to both auto-scheduled and manually scheduled tasks [1].

• Fixed Units. The assigned resources keep the same share of their time. If you add work or units change, the duration moves. Microsoft's example is one person writing a report: give it more days and you have not added people [1].
• Fixed Work. Total person-hours stay put. Microsoft's example is a 300-hour design job that gets shorter as people are added [1]. A Fixed Work task is always effort-driven; you cannot clear that setting [1][3].
• Fixed Duration. The task length does not change when people are added. Microsoft's example is a one-hour weekly status meeting that stays an hour however many attend [1].

What Project recalculates

The task type tells you what stays still. What you also need is what moves. Microsoft publishes the full grid [1]; Figure 2 redraws it. Read across a row: find the task type, find the value you are about to edit, and the cell tells you which value Project will change for you.

View the data

Task type	You edit units	You edit duration	You edit work
Fixed Units	Duration recalculated	Work recalculated	Duration recalculated
Fixed Work	Duration recalculated	Units recalculated	Duration recalculated
Fixed Duration	Work recalculated	Work recalculated	Units recalculated

Two cells deserve attention. On a Fixed Work task, shortening the duration raises the units; on a Fixed Duration task, adding work raises the units. Both can ask more of a person than they have. Microsoft's own worked example shows a full-time person pushed to 125% this way, and Project leaves you to fix the overallocation [1]. Overallocation is the subject of Lesson 18 on levelling; for now, know which edits cause it.

Setting and seeing the task type

To change one task, double-click it to open Task Information, select the Advanced tab and pick the Task type [1]. To change the type that new tasks receive, select File > Options > Schedule and choose from the Default task type list [1]. That changes new tasks only; existing tasks keep the type they have.

Do not rely on opening tasks one at a time. Right-click any column heading in the Gantt Chart table, choose Insert Column and add Type [1][2]. Add Work beside it and you can see the formula at work on every row. To see the units of each assignment, turn on the Task Form under the Gantt: View > Split View > Details. One more detail: cost resources sit outside the formula. Project does not recalculate work or units for cost resource assignments [1].

Screenshot to come

Which type for which owner task

An owner's master schedule has fewer resourced tasks than a contractor's, but the ones it has are often the ones that matter: consultant reviews, commissioning witness time, owner staff training and the owner's own separate contracts. Three rules cover most of them.

• The contract fixes the time: Fixed Duration. A consultant review period set in the specification or contract is a length of time, not a quantity of effort. Adding a second reviewer should not shorten the clock the contract gives.
• The scope fixes the effort: Fixed Work. Witness testing hours taken from a commissioning plan, or installation hours priced by a vendor, are a quantity of work. If people or days change, the hours should not.
• The person's availability is the constraint: Fixed Units. When a staff member can give a known share of their week, keep units still and let the dates follow.

Northgate worked example

Northgate Distribution Centre (fictional) is a 12,000 m² tilt-up warehouse in Vaughan, Ontario, built for Northgate Logistics Inc. (fictional) by Halvorsen Builders Ltd. (fictional) under a CCDC 2-2020 stipulated price contract. The owner keeps its master schedule in Microsoft Project desktop in the file NDC_OwnerMaster_2027-01-11.mpp, on a Monday-to-Friday, 8-hour calendar with Ontario statutory holidays off (see the Northgate fact sheet and Lesson 4).

The task

Under WBS 9, Commissioning and turnover, the owner's scheduler has a task for the owner's commissioning agent to witness fire protection testing: 9.2 Owner's witness testing, fire protection. It starts at M8, commissioning starts, on Mon Nov 1, 2027. The commissioning agent (resource CXA) is assigned at 100% for 10 days, so the task carries 80 hours of work and finishes Fri Nov 12, 2027. All three task types give the same answer at this point. The difference appears when something changes.

Change 1: the agent can only give half their time

The commissioning agent tells the owner that another project needs them every afternoon in November, so units drop to 50%. What Project does depends on the type (Figure 3):

• Fixed Units: units are the edited value, so Project recalculates duration. 80 hours at 4 hours a day is 20 days, finishing Fri Nov 26, 2027.
• Fixed Work: the same result. Work is held at 80 hours and duration stretches to 20 days.
• Fixed Duration: duration is held at 10 days, so Project recalculates work: 40 hours. The bar does not move, and half of the planned witness time has disappeared from the plan.

View the data

Case	Units	Duration	Work	Start	Finish
As planned	100%	10 days	80 h	Mon Nov 1, 2027	Fri Nov 12, 2027
Fixed Units	50%	20 days	80 h	Mon Nov 1, 2027	Fri Nov 26, 2027
Fixed Work	50%	20 days	80 h	Mon Nov 1, 2027	Fri Nov 26, 2027
Fixed Duration	50%	10 days	40 h	Mon Nov 1, 2027	Fri Nov 12, 2027

Change 2: compress the task to 8 days

Go back to the plan (100%, 10 days, 80 hours). This time Halvorsen asks the owner to finish witness testing in 8 days to protect its own commissioning sequence. The scheduler types 8 days:

• Fixed Units: duration is edited, so work is recalculated: 64 hours. The task finishes Wed Nov 10, 2027, with 16 fewer hours of witnessing. Nobody decided to witness less; the type decided.
• Fixed Work: work stays at 80 hours, so units rise to 125%. The commissioning agent is now overallocated, which is exactly the signal the owner needs: compressing the task needs a second witness, not less witnessing.
• Fixed Duration: duration is edited, so work is recalculated: 64 hours, as with Fixed Units.

For this task the scheduler sets the type to Fixed Work. The witness hours come from the commissioning plan, and the owner wants any squeeze on them to show up as an overallocation that someone has to resolve, not as missing hours.

Screenshot to come

Owner's move

• Decide types before loading resources. Set the default in File > Options > Schedule for the file, then set exceptions task by task. Changing types after assignments exist changes the numbers you already have.
• Show the Type and Work columns in the review table. A reviewer who can see type, duration, work and units on one row can predict what the next edit will do.
• Use Fixed Duration for contract periods. Consultant review periods, notice periods and owner approval windows are time the contract gives, not effort.
• Use Fixed Work where the hours are the scope. Witness testing, training and vendor-priced installation are quantities. Let an overallocation flag a squeeze.
• Record the rule. Put the task-type rules in the schedule basis memo so the next scheduler does not reset them.

Common mistakes

1. Treating duration as the only number. On a resourced task, typing a new duration also changes work or units. Check the Work column after every duration edit.
2. Leaving everything on the default. Fixed Units suits some tasks and not others. A review period left as Fixed Units stretches when the reviewer goes part-time.
3. Using Fixed Duration for effort-based work. It keeps the bar still and lets work fall, so lost hours never show on the Gantt.
4. Changing the default and expecting old tasks to follow. The default task type applies to new tasks; existing tasks keep their type.
5. Ignoring the overallocation flag on Fixed Work tasks. It is the type doing its job. Resolve it with people or time, not by switching the type.

Quick quiz

1. Which formula does Project use to schedule resourced tasks?

   1. Duration = Work × Cost
   2. Work = Duration × Units
   3. Units = Work × Duration
   4. Duration = Units ÷ Calendar

2. What is the default task type in Project desktop?

   1. Fixed Duration
   2. Fixed Work
   3. Fixed Units
   4. Effort-driven

3. On a Fixed Duration task, you increase the work. Project recalculates:

   1. Duration
   2. Units
   3. The start date
   4. Nothing

4. Where do you change the task type of a single task?

   1. Task Information, Advanced tab
   2. Task Information, General tab
   3. Project Information dialog
   4. Resource Information, General tab

5. Northgate task 9.2 is Fixed Work at 80 hours, 10 days, 100%. The duration is changed to 8 days. What happens?

   1. Work falls to 64 hours
   2. Units rise to 125%
   3. Duration returns to 10 days
   4. The task becomes Fixed Duration

Show answers and explanations

1. B. Project schedules resourced tasks with Work = Duration × Units [1].
2. C. Fixed Units is the default task type [2].
3. B. On Fixed Duration, editing work recalculates units, which can overallocate a resource [1].
4. A. Double-click the task and use the Advanced tab of Task Information [1].
5. B. Fixed Work holds 80 hours, so 8 days needs 10 hours a day: 125% units [1].

Key terms

Work

The person-hours of effort a resource spends on a task.

Duration

The working time between a task's start and finish on its calendar.

Assignment units

The share of a resource's available time given to one task, such as 50% or 100%.

Task type

The Type field: Fixed Units, Fixed Work or Fixed Duration. It fixes one value of the scheduling formula.

Fixed Work

A task type that keeps total work constant. Always effort-driven.

Overallocation

A resource scheduled for more work in a period than its availability allows.

References

1. Microsoft. Change the task type for more accurate scheduling. Microsoft Support (Project desktop 2016 to 2024 and subscription desktop client).
2. Microsoft. Type fields. Microsoft Support.
3. Microsoft. Change the effort driven setting for task types. Microsoft Support.
4. Microsoft. Learn more about resource units. Microsoft Support.

Verified on November 6, 2026.

Next lesson in this trackEffort-driven scheduling