Add one day (date) to each row instance

I'm trying to do the following with formCalc, but javascript will do as well.  I have a travel expense form with a travel start and end date field.  The difference in days sets the instances of an expense table. I'm trying to get the first row = to the start date; for each subsequent row, I'm trying to add a day to each row.  I've declared a variable to formate the date to a number (var startDate2Num = Date2Num(sf_Header.tbl_Header.Row3.dtd_Start,"YYYY-MM-DD")).  That works; however, I cannot add 1 to each subsequent instance.