I need a field to calculate the Annual Renewal Date of a contract (3 months prior to the End Date) and allow the user to override the Annual Renewal Date value if need be.

Brief:
Field A = Annual Renewal Date (calculated value)
Field A formula: =DATE(YEAR([End Date]),MONTH([End Date])-3,DAY([End Date]))

Field B = Annual Renewal Date (manual date entry)

Question:
So I need field 'A' to automatically calculate the renewal date 3 months prior to 'End Date', unless Field B has a value manually entered into it by the user; in which case Field A would be hidden from the list view.

Is this possible ? I've looked all over the internet for the answer and not been successful.

Additionally, as far as I can tell I can't create a default value field (which is what I wanted to do in the first place) because the Annual Renewal Date is calculated with a field name that can't be referenced (this being 'End Date').

Open to any suggestions.

A calculated field is exactly that; a read only column that derives its value from other columns.

I can't test this now but I'm thinking that the single line of text might be an answer.  In the column settings you can apply a formula here in lieu of using a dedicated column.  I'm not sure if, once an item is edited, whether this can later be overridden.

Hope that's of some help.