Fixed duration task / Effort Driven: Why is the 3rd resource set at 50% by Project?

Occasional Contributor

Resource issue.JPG

I just don't see why Project would assign the 3rd resource as 50%? I use Project 2019 but it's the same in Project 2013. Standard file, no edits in Kalenders or so. Work and Peak values are fine. I am fairly experienced using Project, but can't see this logic. Anyone please?

11 Replies
Ed --

What is the Max. Units value for Piet? If you assign a resource to a task without entering a Units value, Microsoft Project will set the Units value to match the Max. Units value for the resource. Might that explain this mystery? Let us know and we will try to help you.


For multiple resource assignments on a fixed duration, effort driven task, Project will initially equally spread the 3 assignments, so for each of the 3 assigned resources, that's 33% each. After all assignments are made then you can then edit individual assignment levels.




Thanks for the reply, John.

You are exactly right. Looking at the Peak column and work, it works ok. But I don't get why Project assigns the 3rd person only at 50% while I would expect another 100% also. Normal work resource, no max units edit.


I actually train people in Project and get this question sometimes and I would like to be able to explain this.

Hi Dale. Thanks for the reply.
I know what you mean, that is the odd thing here. Max units is standard 100% like the other resources. All 3 equal. I just assigned them, no manual entering values.
Thanks for your help. Could you try and replicate maybe?
best response confirmed by Ed_Ooms (Occasional Contributor)


This "phenomenon" occurs when effort driven is checked (default) for a fixed duration task. The effort driven strives to keep the work content constant and you can see that in the Task Usage view as you assign each of the 3 resources consecutively.


Here's the interesting part. Instead of 3 resources, consecutively assign 4 resources at 100% to the task. As each resources is assigned you will see the Assignment Units replicate the previous resource's units while the Peak adjusts to maintain the constant work value. So for the second assignment, the assignment units is still 100% but the Peak reduces to 50%. Then when the third resource is assigned, the assignment units takes on the peak unit value from the first two assignments (i.e. 50%) and the peak now readjusts to be equal for all 3 assignments (i.e. 33%). If you assign a fourth resource, the assignment units takes on the previous peak (i.e. 33%) and the peak now readjusts to spread the original work content over 4 resources so it shows 25%.


Is this a good enough explanation for your "students"? Don't know, but it might make their heads spin a bit :)


I do recall there was a change to the way peak units are calculated, circa Project 2010 or Project 2013 (I think), but I don't remember the details. Whether that has anything to do with this issue, I don't know.


Wow, thank you! I get it now, I couldn't figure this out. You have been a great help.
For 'students' Tasktypes always make their head spin! Not easy to teach them step by step wha the logic is.
As for the change, in Project 2010 the 'Assigned Units' field stopped being a calculated field and 'Peak' became the calculated value instead. Projectmanagers asked for the original assignment to be visible as a constant value.

You're welcome and thanks for the feedback. To be honest, working with Project often makes my head spin also.

Perhaps the change in the way assigned units and peak units are treated is in play here. The peak is being calculated to maintain the work value while the assignment units is "playing catch-up" as additional resources are added.


All --

I believe you are correct that the new behavior was introduced in the 2010 version of Microsoft Project. And I can tell you that this new behavior led to wholesale confusion among the entire user community, from novice users all the way up to power users.

The new behavior was functionality that Microsoft created for the sole purpose of fixing a bug that had been in the software since Assignments data was introduced sometime prior to Project 2000. When the 2010 version of the software was introduced, I was able to recreate the situation that previously led to a bug in the software, and I was able to see that the new functionality DID successfully resolve the bug. Please don't ask me to explain the bug. It's way too complicated to explain in writing!

Anyway, to resolve the bug, the Microsoft Project development team used the Assignment Units field to capture the original Units value for each resource assigned to each task. And then when a helper was added to an Effort Driven task, the software kept the original value in the Assignment Units field and calculated the new Units value using Peak field. So, Ed, in your example, you can easily see that the Peak field contains the expected Units value for each of the three resources assigned to the task.

I do also want you to know that after Microsoft introduced this new functionality in Microsoft Project 2010, our MVP community loudly and regularly complained to Microsoft about it because of how much confusion the functionality created. We even proposed changes to how the software works as a way to remove the confusion. But in the end, the good folks at Microsoft elected to "stay the course" and keep the software working the same in each successive version.

Anway, hope this historical background helps, for whatever that is worth.
Thanks for updating this thread with your wisdom on the issue. If I could give you credit for the answer (a better one than mine) I would.
John --

Nope, not necessary. Your answer was the best. I just wanted to add some history to explain the seemingly weird behavior of Microsoft Project in this situation. :)

@Dale Howard 

Hi Dale, John,


Many thanks for the additional explanation.
I clearly remember my first Project 2010 version training and explaining Tasktypes. Suddenly there was a different logic and I just stared at the screen, lost :)

This was my very first question at the techcommunity, and it still amazes me the help and worldwide contacts easily available. Thanks!