Duration and Effort (also known as Work) are one of the most confusing topics in project management. Most people confuse duration with elapsed time, the rest with effort. Most questions on Microsoft Project forums also have this misunderstanding as the root cause.

In this blog, we shall look at understanding all these terms in a practical way.


Duration is the working time between a task’s start date and its finish date.

Let’s say Joe works  8 AM – 5 PM (8 hours) Monday through Friday.

Assume Joe is assigned a task that starts on Monday at 8 AM and finishes on Tuesday at 5 PM. What is the duration?

The total working time between the start and finish is 16 hours. That’s the duration.

The elapsed time is 33 hours. That’s not the duration.

Duration in “Days”

Now the next confusion – what is the duration in “days”?

Duration = 16h ÷ 24h = 2/3 = 0.67 days?


Again, we want to consider working time not elapsed time. 24 is the elapsed hours in a day. The working hours is 8.

To convert 16 hours to days. Divide 16 by 8 = 2 days.

If you think about it, it makes intuitive sense – if you are told the duration is 40 hours, you would expect it to be 5d (5 working days).

So, duration in days = duration in hours ÷ work hours in a day.

Some companies work 24 hours per day in shifts, yet they want to “assume” 1 day = 8 hours because it makes more sense to them that way.

In modern project management tools like Microsoft Project or Celoxis (the one we develop), you can input this conversion number.

Effort (also know as Work)

Now let’s address the next confusion – the difference between Duration and Effort.

Effort is the total amount of time a resource will spend working on the task.

If we tell Joe: spend  2hours every day for 5 days on task T, we are asking Joe to spend a total of  2 hours/day x5 days = 10 hours working on this task. The duration of this task is 5 days.

By now, I hope you have understood the key difference between Duration and Effort. The concept is the same in all project management software including Microsoft Project and Celoxis.

Duration, Effort and Allocation for a task are interrelated. I have written another blog explaining this relationship between Duration, Effort, and Units. Check it out!

If you have questions or comments, write them in the section below.

mike hall

Great work! I would like to add my 2 cents: Elapsed duration is the same as "Elapsed time".

shrutika purohit

Nice and informative blog.

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