Computed column type with TODAY
Having a new column type which virtually calculates date differencies based on todays date.
So instead of storing the calculated value inside the database it is just a "virtual" field which is injected into the SQL queries calculating date differences by getting another column as reference - eg DATEDIFF(GETDATE,Birthday column, Days)
How about if you need to perform DateAdd?! Will you ask SharePoint team to implement it in a next release! and wait until they finish it so that you can do your job?! I think it's not a practical solution!
In this case, the role of the calculated column has come to create an on-demand column based on a specific formula that matches your requirements!
By the way, you can achieve your goal through this calculated column formula =DATEDIF([your date column],TODAY(),"d").
For more details, Please, check
- The supported and unsupported columns in SharePoint calculated column formula at https://blog.devoworx.net/2017/09/11/supported-fields-in-calculated-column-sharepoint/
Another workaround is using "JS Link Client-side rendering", For more details, please check