Date tracking using VBA

[apache8119]

I'm trying to keep a record of products that are beyond 30 days. I have the actual check in day in column L4. What I want the code to do is look at that day the product came in and take the difference from todays date. and populate a different cell with the number of days the product has been here. I want it to continue counting until Cell K4 = "complete". I'm not sure where to put this in my VBA or if I have to put it into an equation form and actually add it to the cells throughout my sheet.

Thanks