is Hire Date a date field, a text field or a TimeStamp field?
Assuming that it is a date field, this expression should work :
(Get ( CurrentDate ) - 90 ) < Staff::Hire Date
But the context in which you use this expression and the implementation details can make a difference. Is this a portal filter? A variation of this could be used as find criteria and a different version could even be a match field in a relationship if the terms to the left of the inequality are encoded correctly into an unstored calculation field.
For a timestamp field, you'd need to subtract the equivalent number of seconds, 7776000 seconds = 90 days.
Ok thanks, this one worked perfectly. It finds records only in the 90 day period from hire to day 90.
(Get ( CurrentDate ) - 90 ) ≤ (Staff::Hire Date + 90 ) and (Get ( CurrentDate ) - 90 ) ≤ (Staff::Hire Date) and IsEmpty ( Staff::Termination Date )
By the way, awesome response time Phil! :-D