Data Management Capabilities > Managing Projects > Projects and Programs > Plan Activities > Start Activities
Start Activities
When you start an activity, you set its Actual Start date. How it is set depends on your plan execution type:
Manual—The Actual Start date is set to the Estimated Start date, regardless of whether the two are the same.
Automatic Execution—The Actual Start date is set to the current date and time.
Summary activities start when their earliest child activity starts. Otherwise, there are several ways to start the activity:
Open the Track Work window for the activity. Enter a value into the Actual Work field or the % Work Complete field.
If an activity has resource assignments, then an assigned resource can start the activity by tracking work for their resource assignment task. Open the Track Work for Selected Assignments window and enter a value into the Actual Work, % Work Complete, or Remaining Work field.
This action is only available in automatically executed projects, and it appears for activities that have not yet started but do not have any obstacles (such as a predecessor or constraint type) that would prevent the activity from starting.
In automatic execution mode, activities automatically start when they reach their Estimated Start date.

Automatically Executed Plans
If you are working in an automatically executed plan, then you can only start and track work for eligible activities.
There are several reasons why you might not be able to start an activity, including the following:
The activity is the dependent task in a Finish-to-Start predecessor relationship, and its predecessor has not been completed. Or it is the dependent task in a Start-to-Start predecessor relationship, and its predecessor has not yet started. For more information, see Predecessor Relationships.
The activity constraint type is Start No Earlier Than, and the constraint date has not been reached. For more information, see Activity Date Constraints.
To start an activity, the project must be in the Running state and the plan in the In Process state. For more information, see Automatic Execution.