What happens if I tick the effort driven checkbox?

When you assign or remove people from a task, MS Project lengthens or shortens the duration of the task based on the number of resources assigned to it but it does not change the total amount of work for the task. This is called effort-driven scheduling.

Effort-driven and non effort-driven

For understanding the difference between effort-driven and non effort-driven, think of the following question: "Divide or double up?". This relates to the total work on the task;
  • Suppose an 8-hour paint task you are doing alone, and now a second person is added. Should the total work be divided between these resources, so 4 hours of work each? Or should they both work 8 hours now? If the work should be divided (total amount of work stays the same), this is effort-driven.
  • Suppose you are on an 8-hour business flight. If you bring a colleague along, should the work be divided, so they fly 4 hours each? Or should they both fly 8 hours, so the total amount of work is now 16 hours? Increasing the amount of work when adding an extra resource is called non effort-driven.
Effort-driven scheduling only takes effect when resources are added to or removed from a task. Effort-driven calculation rules are not applied when you change work, duration, and unit values for resources already assigned to a task. Fixed work is always effort driven, for fixed duration or units you can choose (checkmark) whether or not new tasks are effort driven.
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