Entering an Actual Start that is earlier than the Scheduled Start, say by 1 hour, is adding the 1 hour to the duration field instead of decrementing the finish date by 1 hour.

  • 1
    Check your constraints. Do you have a must finish on constraint on that task? Jun 26, 2015 at 21:10
  • Just setting an actual start date isn't much for Project to go on. Do you have resources assigned to the task? Have you entered any other progress information other than Actual Start date? I am not seeing the duration field increase in any scenario.
    – JulieS
    Jul 1, 2015 at 20:05
  • What is the question?
    – MCW
    Oct 3, 2016 at 10:35

2 Answers 2


One office help entry states that "Entering an actual start or finish date for a task changes the corresponding scheduled or planned date for that task."

Perhaps by setting the actual start, you've changed the scheduled/planned start, but the scheduled/planned end stays the same, resulting in a longer duration (I would expect this behavior if the task is manually scheduled). Since you've entered it manually, Project may just think you're trying to edit the start only, and calculates the duration to match.

An alternative might be to change the scheduled/planned start to the actual date, and instead compare to baseline to show how the schedule has improved.


Uncheck the "split inprogress task" option. In my case, this solved the problem.

I'm moving from p6 to ms project. I never really liked this feature.

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