You still haven't told me which finish date you're talking about changing -
the scheduled Finish in the Gantt chart entry table, the baseline finish, or
the actual finish - the specific answer to your question is dependent on
which "finish date" field you're planning on entering the data into. But in
any case you don't need to figure out actual duration by hand. If you're
setting the task complete and the actual duration differs from the scheduled
duration and you want Project to calculate the real duration for you,
display the Tracking Table (View menu, Tables, Tracking) and enter the date
work actually commenced on the task in the Actual Start column and the date
work was completed in the Actual Finish column. Project will take those two
values and calculate the Actual Duration, set the Remaining Duration to
zero, mark the task 100% complete, and transfer your input values back into
the regular Gantt chart entry table's Start, Finish, and Duration columns.
HOWEVER, entering those same values directly into the entry table's Start,
Finish, and Duration columns WILl NOT post that there has been any progress
to the task, it simply means it's still waiting to be done but you have
revised the estimates you'd previously made regarding it.
So there is no technical reason you can't enter the Actual Finish date in
the appropriate field - in fact, I recommend it. OTOH there is a very good
reason to not enter it into the baseline finish - baselines are supposed to
be snapshot records of what you originally planned so you can see if your on
track or not. Likewise, there's an excellent (technical) reason not to
enter the actual finish in the Finish column of the Gantt chart entry
table - doing so does not post in any actual progress but simply indicates
the plan has been revised.
HTH
--
Steve House [MVP]
MS Project Trainer & Consultant
Visit
http://www.mvps.org/project/faqs.htm for the FAQs