It can be really nice to create a computed column and add it to the table rather than adding it in a field
This would work well using the function listed in the previous post where I automatically calculate the age of trees.
ALTER TABLE dbo.t001trees ADD treeage AS (dbo.functionyearmonthday(dbo.t001trees.plantdate, GETDATE()));
This will appear in the table and look like it is an actual field but it is calculated and will not keep the figures in the table unless you specify persistance
see the above link for further reading on this topic