mmm-yy Date format for end of month?

[dropkickweasel]

I'm working on a workbook that is used to track the inventory and expiry dates of products.
As new stock is added to the workbook, the expiry dates are formatted as "mmm-yy".
I believe this is treated by Excel as being the first of the specified month.
However, all of the products go out of date at the end of each month.

Is there any way to change the way Excel perceives "mmm-yy" so that it is treated as the last day of each month, rather than the first?

The intended next step of this process is to apply conditional formatting to show when products are within X months of their expiry date, will expire at the end of the current month, or have expired.

Thanks in advance for any contributions before I start trying to improvise.

 

[Fluff]

Glad we could help & thanks for the feedback.