rbruza,
I thought a little more about your question and I believe this is more of what you are wanting to do. The function below should do what you are wanting to do. The code needs to go in a regular module in the VBA editor.
On your worksheet you will use projdays(Start Date, Number of Days). Of course this can be a cell references where you have the date and number of days listed on your worksheet.
I have not dealt a whole lot with functions, but this appeared to work on my end. Hopefully, it will do what you are wanting it to do. Let me know what happens.
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