Hi, today I am going to clarify one important thing which bothers a lot of  of my Blog readers. I will go step by step through example and explain them.

First I’m going to build simple Project:

Now I will create three Resources:

and I will assign them to Tasks:

I will now make Task 1 as 25% completed:

Task 2 actually starts earlier than planned (that is, earlier than its current Start Date). So Task 2 Actual Start Date is manually updated to an earlier date.

In the Mark on Trask -> Update Tasks dialog box I will enter 25% Complete , the earlier Actual Start Date for Task and click OK:

and:

and I will get:

Now, I will put status date to 24.07.2018, and then I will update the project to reschedule uncompleted tasks to after the Status Date:

and:

and I will get:

The Actual Start Dates of Task 1 and Task 2 are not changed, but their Finish Dates are changed for the later dates. That is  OK! Why? Start date is not changed because some work is already done and it was started at those Start Dates, so they cannot be moved or changed. What is done is DONE! It is written in the stone!

And now, where my blog readers have the biggest problem? Look at this.

I will make  Task 2 100% complete based on its earlier Actual Start Date and original Duration, so I will enter the Actual Finish Date in the Update Tasks dialog box:

Finally, I will get:

the question is: The Duration for this task is shown only 0.75 days instead of  its scheduled Duration of  3 days?

At the first look, it seems that this is a bug, because Start Date id 24.07.2018, finish Date is 26.07.2018, but Duration is 0,5 days instead of 3 days. But this is not a bug. I will explain why this is totally normal result:

1. First I put 25% Completed for the Task 2 which had 3 days Duration. It means that actual Duration is 25% of 3 days is 0,75 days
2. Then I moved the all unfinished Tasks after the status date, which is 24.07.2018.
3. Because Task 2 has Finish to start relationship with Task 1, and Task 1 was supposed to finish at 27.07.2018, and the remaining part of Task 2 is supposed to start at that date (27.07.2018)
4. BUT! I put 100% at %Complete, and Finish date to 26.07.2018. which is before Task 1 was finished.
5. This means that Task 2 has no work left, so it was needed only 25% of original estimated work, and this is 0,75 days and 6 hours! If you have expected that those 2 days (25.07.2018, and 26.07.2018) work will be performed, you were wrong and this is because nothing is supposed to be done at that dates because Task 1 was not finished at that time. So the earliest date on which work on Task 2 is supposed to be done is 27.07.2018, and this is before the finish date of Task 1 which is 26.07.2018

Hope this helps.

Regards!