Found awesome article on Ariba connect blog title "Equations on Two Date Fields in Reporting [User-Defined Fields]: Derive a Document's Age, Duration of its Status, Days until Expiration, etc."
https://connect.ariba.com/AC_ATC_Blog_OD/1,,MDAxNzk0NTQyNA==,00.html#Article&155054
I think it answers my questions for now.
Today(), Now() is referenced with CURRDATE in Ariba. That's the day the report is run.
Formula is then something along the lines:
sum(CURRDATE-EffectiveDate.Day)
or if I want to count projects that are less than 90 days old
sum(if(CURRDATE-EffectiveDate.Day<90,1,0))
Br
Chr