I have a fixed-duration task in MS Project that is 2 days in duration and 8 hours of work. When I assign a resource to the task, the resource units are automatically set to 50%. If I change the resource units to 100%, the work is automatically changed to 16 hours.

However, if I set the work back to 8 hours, an error dropdown says "You decreased the amount of work for this task" and gives me 2 options:

  1. Decrease duration but keep the hours resources work per day (units) the same.
  2. Decrease the hours resources work per day (units) but keep the same duration.

Now, if I choose option 2, nothing actually changes, and I don't see any errors. Why is this allowed?

1 Answer 1


The work equation always applies to task resource assignments: Work = Units x Duration

When you cut the work in half (from 16 to 8), then MSP has to reduce either Units or Duration to balance the equation. For a Fixed-Duration task, the Duration is held constant by default, and the Units are reduced automatically. This default change is kind of held in a buffer while the pull-down alert gives you the opportunity to override it by selecting option 1. (Selecting Option 2 simply leaves the default response intact.)

Similar alert/default/buffer responses are raised any time you change (after initial entry) one of the three components of the work equation, with their precise behavior depending on the task type (FD, FU, or FW). You can always choose to ignore these alerts.

  • I would expect to see units changed to 50% after I select Option 2, correct? What I'm confused about is that after selecting Option 2, I'm left with units set at 100% (and duration remaining at 2 days and work remaining at 8 hours). This doesn't balance the work equation, and yet I see no errors.
    – Andrew
    May 23, 2019 at 5:44
  • Yes, that is what you'd expect, and that is the behavior of all versions up through MSP2010 (and I think MSP2013). With more recent MSP versions, the base resource assignment units is (sometimes) left unchanged for FD tasks even though the work is correctly re-distributed. In that case, the assignment's "Peak" value is the only valid indicator of the actual assigned units. The change was made to fix an issue somewhere else. You can find more detail on technet.
    – Tom Boyle
    May 23, 2019 at 13:37

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