Percentage Complete - Excel 2010 - dates comparison

I'm trying to figure out how to compare 2 dates and provide a percentage complete.

Cell Q5 = estimated date for completion by the supplier

Cell D2 = Today() function

Cell P5 = simply lead time calculation

I need to compare cell Q5 with either D2 or P5 to give a estimated percentage complete. This will then show where the supplier should be on a simple timeline, once they go late, i'd expect it to go late or report. The percentage output would go into Cell N5.

Cell O5 = Inputted by the suplier, the actual date completed, this can't be completed until we acknowledge work complete, so for the majority of the time the cell will be empty.

Any ideas?