combine 2 functions

[Johnwats]

On a Form i have 3 boxes to keep check on students progress, 1) Course
started, 2) Course completed, 3) Days in progress. Once i have entered a
date in box 1, i can enter a DateDiff function in box 3 & that works fine.
But when i enter a completed date in box 2, i want the Days in progress box
to stop counting. I have been told to use a DateDiff & IIf functions
combined, but i just can't get the syntax correct. Any help appreciated.

John W

 

[Johnwats]

I am entering the function in the "days in progress" box. But can't get it
to stop counting to the current date, even when there is an earlier date
entered in the "completed" box.