Working with the WORKDAY function

I'm a beginner at the use of excel,I am writing to ask for your assistance as I having being get request from my colleagues to help create procurement process tools using excel, I have done some but I'm having troubles with one at the moment and I fear there will be more in the future. Attached within is the sample process of a workflow, tracking the dates on every milestone till the due date. I used the WORKDAY function and I was able to achieve the due date result by allowing users change the "DAYS" variable fed into the WORKDAY function in a cell above each milestone date, so altering each milestone day the date changes hence also altering the due date, on presenting this to my manager he had comments and changes, he wants people to be able to input dates to affect the due date instead of the previous one I did where they are allowed to input days to affect the due date. so basically i see having to re write a VBA code for the workday function [FONT=Segoe UI, Segoe UI Web Regular, Segoe UI Symbol, Helvetica Neue, BBAlpha Sans, S60 Sans, Arial, sans-serif]WORKDAY(start_date, days, [holidays]).Please i would appreciate any help to achieve this thanks.[/FONT]

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Attachment included

Attached within is what i tried working on.

I am afraid I don't get what you need to do, or why you think tat you need VBA.

Can you tell us what your manager wants to change, an example of a cell on the sheet, and what you want the effect to be, again in terms of what happens on the sheet?

Ok, I will give an instance with an online store. the order process is as follows: 1. client places an order (duration 1 day) 2. store packs client' order (duration 1 day) 3. store ships order (duration 2 days) 4. order reaches destination and client pick up (duration 1 day) in total the due date for client to receive goods is in 5 days, lets assume the client places and order today 2nd of March 2015 the client should receive his order on the 9th of March 2015 (working days only) as long as the duration period for each milestone is in place. if there is a delay in shipment which originally takes 2 days and now takes 4 days the new client pickup date/due date will change to the 11th of March. On getting this notification my manager wants to put in a certain date to determine any clients pickup date and dates on every milestone (1 - 4) so as to create room for any shipment delay/fast response or any delay/fast response on any of the milestones , he also want to wants to make the shipment mode (either by air or sea) to be a determining factor for the duration selecting by a drop down pick.

The sheet has more milestones so the instance i gave is the summary, and i hope i made more sense than my previous message.