Hi Marlon
Try to use below concept
1. from a date try to get a first day of the year (i.e just (01-01-year(date))
2. Get number of days between these 2 days(N) now N+1= Day number in year
3. Finally concatenate your year and number of days.
=FormatNumber(Year([Today]);"0000")+(FormatNumber(DaysBetween(ToDate(concatenation("01-01";FormatNumber(Year([Today]);"0000"));"mm-dd-yyyy");[Today])+1;"000"))
Replace [Today] in above formula with your object in report.