I have month in one column many times by a different product i.e. January,
February, March etc.....in another column I have date sale kicked in say
March.
In another column I have projected sales for one month. How can I have the
worksheet convert the month to a number so I can calculate sales for December
minus the month I started the sale of a product i.e. if we started in March
this would be projected at 12-3 or 9 months of sales times the amount of the
sales per month. I need to do this for multiple products and cannot figure
out how you use a month that someone keys into a spreadsheet in a calculation
since it could change each line by line.

Any help is much appreciated.