Set your defaults as below:
Start
=DateAdd(DateInterval.Year, -1 , DateSerial(DatePart("yyyy",Today), 1, 1))
End
=DateAdd(DateInterval.Day, -1 , DateSerial(DatePart("yyyy",Today), 1, 1))
The DateSerial() determines the first day of the current year. Then either subtract one year or one day to get the start and end dates.
Scott