I'm trying to calculate periodically sales for new products, which have been in the market for max 6 monts. After that 6 months the sales of the product is not to be calculated. I have a huge amount of products, where this information should be calculated, so manually calculating is not an option. The products are in rows, and periods are in columns. As the data concerns several years data there is a problem, that some products have in some months zero sales, and in the next month again some sales. This messes up always my calculations. How to truly take only the first 6 months, and leave all the rest uncalculated?

How should I do this? Sorry, I tried, but wasn't able to put an example here...

Many thanks for your help,

Erza