mysql workbench – How to create a calculated field that stores the number of days remaining according to the date difference?

I am working with a Rent-a-Car System, and I need to know how much time is left for a Client, for this I want to create a calculated field that is generated from the current date (of the system) and the Date_Final.

SELECT DATEDIFF (Date_Final, CURDATE ()) this query gives me what I'm looking for, but when I save it in a column that is generated automatically, it gives me the following error: ERROR 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'select datediff (Date_Final, CURDATE ())) STORED'

Any recommendation please?