Estimated duration is not changing based on work hours

The issue you’re seeing is actually expected behavior in Microsoft Project when no resources are assigned to a task. Here’s why your duration isn’t updating:

1. No resources = no calculation
   • Project calculates Duration = Work ÷ (Units × Hours per day).
   • If no resource is assigned, Project doesn’t know the units to use, so duration stays fixed regardless of the work value.
   Fixed Units & Effort-Driven settings Make sure the task type is Fixed Units.

     Check **Effort-Driven** in the task’s Advanced tab—this allows duration to adjust when you assign resources.
   
     **Auto-Scheduled tasks**
   
        Manually scheduled tasks won’t recalc automatically. Switch to **Auto Schedule** for correct behavior.
   

Solution:

Assign at least one resource at 100% availability.

Enter your work value (e.g., 180 hours).

Project will now calculate the duration correctly.

Adding a second resource will reduce duration proportionally if Effort-Driven is enabled.

Example:

1 resource, 80 hours → Duration = 10 days (8 hours/day)

2 resources, 80 hours → Duration = 5 days

Until a resource is assigned, Project can’t spread work over days, which is why your durations weren’t updating.The issue you’re seeing is actually expected behavior in Microsoft Project when no resources are assigned to a task. Here’s why your duration isn’t updating:

No resources = no calculation

Project calculates Duration = Work ÷ (Units × Hours per day).

  If no resource is assigned, Project doesn’t know the units to use, so duration stays fixed regardless of the work value.
  
  **Fixed Units & Effort-Driven settings**
  
     Make sure the task type is **Fixed Units**.
     
        Check **Effort-Driven** in the task’s Advanced tab—this allows duration to adjust when you assign resources.
        
        **Auto-Scheduled tasks**
        
           Manually scheduled tasks won’t recalc automatically. Switch to **Auto Schedule** for correct behavior.
           

Solution:

Assign at least one resource at 100% availability.

Enter your work value (e.g., 180 hours).

Project will now calculate the duration correctly.

Adding a second resource will reduce duration proportionally if Effort-Driven is enabled.

Example:

1 resource, 80 hours → Duration = 10 days (8 hours/day)

2 resources, 80 hours → Duration = 5 days

Until a resource is assigned, Project can’t spread work over days, which is why your durations weren’t updating.

Hi @Emily Platt,

Thank you for posting your question in the Microsoft Q&A forum. 

I understand that you're encountering a common misunderstanding in Microsoft Project where task duration isn't recalculating based on work hours, even though you're using the Fixed Units task type and have "Estimated" checked for duration. 

Let me explain some key points why duration isn't updating based on this document: The duration or work value changed when I assigned a resource - Microsoft Support

1. No Resources Assigned = No Work Calculated If you haven’t assigned any resources to the task, Microsoft Project has no way to calculate work or adjust duration. Even if you enter 180 hours of work, without a resource (and their availability), Project doesn't know how to spread that work across time.
2. Fixed Units Task Type Behavior in a Fixed Units task:
   • Work = Duration × Units
   • If you change Work, Project recalculates Duration (assuming Units are fixed).
   • But again, this only works if a resource is assigned.
3. "Estimated" Duration Checkbox This checkbox only flags the duration as tentative, it doesn’t trigger recalculation. It’s more of a visual cue than a functional one.
4. Effort-Driven Setting If the task is not marked as Effort-Driven, adding resources won’t reduce the duration. You can check this by:
   • Double-clicking the task → Advanced tab → Ensure Effort Driven is checked.

To recalculate properly, I'd recommend you follow these fixes:

1. Assign at least one resource to the task.

• Example: Assign a resource at 100% (full-time).
• Then enter the Work value (e.g., 180 hours).
• Project will now calculate the Duration based on the formula.

2. Ensure Task Type is set to Fixed Units:

• Right-click column header → Insert Column → Add Type column.
• Set the task type to Fixed Units.

3. Check Effort-Driven setting:

• Double-click the task → Go to Advanced tab → Check Effort Driven.

4. Use Auto-Scheduled Tasks:

• Manually scheduled tasks don’t always recalculate duration/work.
• Switch to Auto Schedule mode for accurate calculations.

For example, let’s say:

• You assign 1 resource at 100% (8 hours/day).
• You enter 80 hours of work.
• Project will calculate: Duration=80 hours/ (1 unit×8 hours/day) =10 days

If you then add a second resource at 100%, the duration becomes: 80/ (2×8) =5 days

Note: Please understand that our initial response does not always resolve the issue immediately. However, with your help and more detailed information, we can work together to find a solution. 

I hope this information is helpful. Please follow these steps and let me know if it works for you. If not, we can work together to resolve this. 

Thank you for your patience and your understanding. If you have any questions, please feel free to reach out. 

I'm looking forward for your reply. 

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