In a blank column in the query design grid, type (verbatim):
Upcoming_Birthday: IIf(CDate(Format([Birthday], "m/d") & "/" & Year(Date())) < Date(),
CDate(Format([Birthday], "m/d") & "/" & (Year(Date())+1)),
CDate(Format([Birthday], "m/d") & "/" & (Year(Date()))
That's called a calculated field...