Defining a date within the button shortcode

I need to define a date within the button that the membership runs yearly from specific dates.

This for example would be 15/06/YYYY to 14/06/YYYY

I also need to give the button a price for

A) The first 6 months of the membership from 15/06/YYYY – 14/12/YYYY

B) The last 6 months of the membership 15/12/YYYY – 14/05/YYYY+1

I don’t mind changing the button costs manually half way through the year if this is easier as we will have many different memberships.

I understand from other posts that I need to call a PHP file to work out the date and then call this in the shortcode but has anyone achieved this so that I can change the code to suit my needs?

Thanks in advance

*Bump*