PersianCalendar pc1 = new PersianCalendar();
PersianCalendar pc2 = new PersianCalendar();
var date1 = pc1.ToDateTime(1395, 01, 01, 0, 0, 0, 0);
var date2 = pc2.ToDateTime(1396, 01, 01, 0, 0, 0, 0);

datetTime.Text = (date2 - date1).TotalDays.ToString();