Durations and estimates in Microsoft Project

A duration is the most common number in a schedule and the one people check least. Microsoft Project reads "5" as five working days, "5ed" as five calendar days around the clock, and "5d?" as a guess you have not confirmed yet. This lesson explains how Project measures durations, how elapsed and estimated durations work, and how an owner should estimate, record and challenge the durations in a master schedule.

Learning outcomes

• Enter durations in minutes, hours, days, weeks and months, and explain how the Hours per day, Hours per week and Days per month settings convert between them.
• Use elapsed durations correctly, and explain why they ignore the project calendar.
• Use the question mark to flag estimated durations, find them with a filter, and clear them when a duration is confirmed.
• Choose between analogous, parametric, three-point and expert-judgement estimates for an owner's master schedule.

The lesson

What a duration means in Project

In Microsoft Project desktop, a task's duration is the span of working time between its start and its finish. Nonworking time, such as weekends, holidays and the hours outside the working day, does not count. Project combines it with the calendar, dependencies and constraints to place every automatically scheduled task, so the calendar from lesson 4 must be right first: a 10-day task over the Victoria Day weekend finishes a day later than in mid-June. Duration is also not work: a two-person crew does 32 hours of work in a 2-day duration. Work and resources come later in the track.

Duration units and how to type them

You enter a duration by typing a number and, optionally, a unit in the Duration column of the Gantt Chart view. Microsoft documents five abbreviations: m for minutes, h for hours, d for days, w for weeks and mo for months. A number with no unit uses the default, days, set under File > Options > Schedule in the Duration is entered in list. Leave it on days.

Project stores durations as working hours. Three boxes in the Calendar options for this project section of the same page set the conversion: Hours per day, Hours per week and Days per month, by default 8, 40 and 20. They do not change the calendar; they only define what a "day", "week" and "month" mean.

The settings must match the calendar. Set Hours per day to 10 on a site working 8-hour days and a "1d" task spills into a second day; set it to 7.5 and durations start showing decimals. Check these numbers in every file you did not build. And avoid months: an Ontario month has roughly 19 to 23 working days once holidays are removed, but "1mo" is always 20. Days are unambiguous and match how contractors report.

Elapsed durations

Add an e in front of any unit and the duration becomes elapsed: em, eh, ed, ew and emo. An elapsed duration runs 24 hours a day, seven days a week, and ignores the project calendar, including weekends and statutory holidays. One elapsed day is 24 hours, one elapsed week is seven days, and one elapsed month is 30 days.

Use them for things that happen whether or not anyone is on site: concrete curing, drying periods, or a response time stated in calendar days. Never use them for crew work or assign people to them; Project would schedule people around the clock. Figure 1 shows how far the two kinds of day drift over a long weekend.

View the data

Entry	Start	Finish	Why
7d	Thu May 20, 8 a.m.	Mon May 31, 5 p.m.	Skips weekends and Mon 24
7ed	Thu May 20, 8 a.m.	Thu May 27, 8 a.m.	168 hours straight
3d	Fri May 21, 8 a.m.	Wed May 26, 5 p.m.	Fri, Tue, Wed
3ed	Fri May 21, 8 a.m.	Mon May 24, 8 a.m.	72 hours straight

A successor still starts on its own next working time: a cure that ends at 8 a.m. on a Sunday lets the crew start Monday, not Sunday.

Estimated durations and the question mark

Type a question mark after any duration, such as "15d?", and Project marks it as an estimate. The task's Estimated field turns to Yes. Remove the question mark, or clear the Estimated check box on the Advanced tab of Task Information, and the duration becomes confirmed. New automatically scheduled tasks start as "1 day?" by default, so a fresh task that nobody has estimated is easy to spot.

Two settings under File > Options > Schedule control this. Show that scheduled tasks have estimated durations displays the question marks. New scheduled tasks have estimated durations gives each new task that "1 day?" placeholder. Leave both on in an owner's file. To list every estimate, apply the built-in Tasks With Estimated Durations filter (View > Filter), or add the Estimated column and sort or group by it.

The question mark is a flag, not a calculation: Project schedules "15d?" exactly like "15d". Its value is honesty about which numbers are still placeholders. (Manually scheduled tasks accept text such as "TBD", but they ignore logic; use a number with a question mark instead.)

Screenshot to come

Where durations come from: four estimating methods

Project records a duration; it cannot tell you whether it is right. Four methods cover nearly every case.

• Analogous estimating. Take the actual duration from a comparable past project and adjust it for size and complexity. Fast, and only as good as the comparison.
• Parametric estimating. Divide a quantity by a production rate: square metres of slab by square metres per pour, panels by panels per crane day. Reliable when both numbers have a source.
• Three-point estimating. Ask for an optimistic (O), most likely (M) and pessimistic (P) duration. The beta-weighted (PERT) mean is (O + 4M + P) / 6, and (P − O) / 6 gives a rough standard deviation. Use it where uncertainty is the main story.
• Expert judgement and bottom-up. Ask the people who will do the work, ideally by breaking the task into pieces they can each estimate. For contractor work, the contractor's own schedule is the bottom-up estimate.

Whatever the method, write it down. The GAO Schedule Assessment Guide expects durations to rest on the same rationale, data and assumptions as the cost estimate, and to be short enough to measure progress; the DCMA 14-point assessment flags incomplete activities over 44 working days. A line in the task's Notes field turns a number into evidence. Figure 2 helps choose a method.

Northgate worked example

It is January 2027. The owner's PM for Northgate Distribution Centre (fictional) has the owner's master schedule, NDC_OwnerMaster_2027-01-11.mpp, with the Northgate calendar from lesson 4 and the summary WBS from lesson 5. Halvorsen Builders Ltd. (fictional) does not owe its baseline until Wed Feb 10, 2027, but the owner needs durations now.

The PM first confirms the Schedule options: days; 8, 40 and 20 to match the 8-hour Northgate calendar; both estimated-duration options ticked.

Step 1: milestone-window placeholders with a question mark

For the construction phases, the PM enters durations measured from the Northgate milestone windows, each with a question mark, because they are the owner's reading of the target dates, not Halvorsen's plan. (On a repeat building type the PM would cross-check them analogously against a past warehouse.) Two examples:

• 3 Foundations and slab-on-grade: M3 mobilization Mon Mar 1 to M4 Fri May 14, 2027 is 54 working days on the Northgate calendar, because Good Friday (Mar 26) is a holiday. The PM enters 54d?.
• Tilt-up panels to M5: Mon May 17 to Fri Jun 25, 2027 is 29 working days, not 30, because of Victoria Day (May 24). The PM enters 29d?.

Both exceed 44 days. That is acceptable for planning placeholders, and the question mark says so; Halvorsen's detailed activities will replace them.

Step 2: an elapsed duration where the calendar does not apply

Tilt-up panels are cast on the slab and must reach the specified strength before lifting. The PM adds an illustrative 7ed? panel cure between casting and erection: elapsed, because concrete gains strength over weekends, and estimated, because the specification and the engineer's lift criteria govern the real period.

Step 3: a three-point estimate for an owner risk

Permanent power (M7, Fri Oct 1, 2027) depends on the local electricity distributor's design and connection work, which neither the owner nor Halvorsen controls. The PM asks the electrical engineer for three durations, in working days, from the distributor accepting the application to energizing the service. Figure 3 shows the result.

View the data

Value	Working days
Optimistic (O)	40
Most likely (M)	55
Pessimistic (P)	90
Beta mean (O + 4M + P) / 6	58.3
Standard deviation (P − O) / 6	8.3

The PM enters 58d? and writes the three values in the task note. The spread is the message: the pessimistic case is 32 working days past the mean, so the application must go in early enough that a slow response still supports permanent power on Oct 1. The PM adds an owner action to confirm the application date with Ridgeline Architects Inc. (fictional).

Step 4: review and clear

Before each monthly report the PM applies the Tasks With Estimated Durations filter. Once Halvorsen's baseline is accepted, anything still flagged is an open question with an owner, not a forgotten default.

Screenshot to come

Screenshot to come

Owner's move

• Require working days. In the contract schedule specification, ask for durations in working days, with elapsed durations allowed only for cure, drying and similar non-work periods, each one named in the schedule narrative.
• Ask for the basis of long or critical durations: quantity and rate, past job, or crew judgement.
• Check the conversion settings on every native file you receive.
• Report the count of estimated durations in your own file each month. It should fall steadily after the baseline is accepted.

A duration without a basis is an opinion. Put the method and source in the task note.

Common mistakes

1. Typing months. "3mo" is always 60 days at the default setting, whatever the calendar holds. Use days.
2. Elapsed durations for crew work. "10ed" schedules a crew through weekends and holidays.
3. Changing Hours per day to fix a calendar. The Schedule options do not change working time. Fix the calendar under Project > Change Working Time instead.
4. Leaving "1 day?" placeholders. A forgotten default looks like a real one-day task and can sit on the critical path unnoticed.
5. Treating the question mark as a buffer. Project schedules "15d?" the same as "15d". If you want contingency, show it explicitly.

Quick quiz

1. With default settings, what does Project store when you type "2w"?

   1. 14 calendar days
   2. 80 working hours
   3. 2 elapsed weeks
   4. 40 working hours

2. Which entry runs through weekends and statutory holidays?

   1. 5d
   2. 5d?
   3. 5ed
   4. 1w

3. What does the question mark in "15d?" change in the schedule calculation?

   1. Nothing; it flags the duration as an estimate
   2. It adds 15 percent contingency
   3. It makes the task manually scheduled
   4. It removes the task from the critical path

4. Optimistic 40, most likely 55, pessimistic 90 days. What is the beta-weighted (PERT) mean?

   1. 55.0
   2. 61.7
   3. 58.3
   4. 65.0

5. The calendar has 8-hour days, but Hours per day is set to 10. What happens to a new "1d" task?

   1. Nothing; the calendar overrides it
   2. It needs 10 hours and spills into a second working day
   3. It becomes an elapsed task
   4. Project changes the calendar to 10-hour days

Show answers and explanations

1. B. At 40 hours per week, 2w is 80 working hours.
2. C. The "e" prefix makes a duration elapsed, ignoring the calendar.
3. A. It sets Estimated to Yes; dates are unchanged.
4. C. (40 + 4 × 55 + 90) / 6 = 350 / 6 = 58.3.
5. B. "1d" becomes 10 hours, but the calendar offers 8 a day, so the task finishes on day two.

Key terms

Duration

The span of working time between a task's start and finish, excluding nonworking time.

Elapsed duration

A duration entered with an "e" prefix (em, eh, ed, ew, emo) that runs around the clock and ignores the project calendar.

Estimated duration

A duration followed by a question mark, which sets the Estimated field to Yes without changing the calculation.

Analogous estimating

Estimating from the actual duration of a comparable past activity, adjusted for differences.

Parametric estimating

Estimating by dividing a quantity by a production rate.

Three-point estimate

An estimate built from optimistic, most likely and pessimistic values, often combined as (O + 4M + P) / 6.

References

1. Microsoft Support, Change a task duration.
2. Microsoft Support, Duration (task field).
3. Microsoft Support, Estimated (task field).
4. Microsoft Support, Change the default task duration unit.
5. Microsoft Learn, Application.OptionsCalendar method (Project).
6. Microsoft Learn (archived), Task.DurationFormat enumeration.
7. MPUG, Thinking about elapsed durations.
8. U.S. Government Accountability Office, Schedule Assessment Guide: Best Practices for Project Schedules (GAO-16-89G), Best Practice 4.
9. Deltek Acumen help, DCMA 14-Point Assessment metric descriptions.

Verified on November 4, 2026.

Next lesson in this trackDependencies: FS, SS, FF, SF