sharepoint designer – Custom List Column Validation in SP2013

I have encountered a small problem when I want to validate my fields (columns) in my custom list in Sharepoint 2013.

I give you an example:

I have a custom form made in Infopath with multiple fields and 2 date and time fields. We call it "StartDate" which never changes and the other is "EndDate" and this date changes. And when I have the form "createListItem", the validation "EndDate" must be "StartDate + 365days", which is quite easy to do. But when I need to edit an item from the list, I need another validation of "EndDate", this time "EndDate + 365days". Is it possible to do it without programming? I tried it using additional fields and calculated field types, but I was not able to get what I wanted.

No suggestion? Maybe someone here was trying to do the same thing.

Thank you in advance.