Here is the FormCalc example....how to do it...I used this code in "docReady" event of StartDate.
if (StartDate.isNull) then
var thisYear
var nextYear
thisYear = Num2Date(Date(), "YYYY")
nextYear = Num2Date(Date(), "YYYY")+1
var sDate
var eDate
sDate = Date2Num(concat("07/01/", thisYear), "MM/DD/YYYY")
eDate = Date2Num(concat("06/30/", nextYear), "MM/DD/YYYY")
//xfa.host.messageBox(sDate);
//xfa.host.messageBox(eDate);
StartDate.rawValue = Num2Date(sDate, "YYYY-MM-DD")
EndDate.rawValue = Num2Date(eDate, "YYYY-MM-DD")
endif