Dim [date] As String = "1389/02/27"
Dim year As Integer = Integer.Parse([date].Substring(0, 4))
Dim month As Integer = Integer.Parse([date].Substring(5, 2))
Dim day As Integer = Integer.Parse([date].Substring(8, 2))
Dim p As New System.Globalization.PersianCalendar()
Dim dt As DateTime = p.ToDateTime(year, month, day, 0, 0, 0, 0)
dt = dt.AddDays(1)
Dim pr As New System.Globalization.PersianCalendar()
Label1.Text = ((pr.GetYear(dt).ToString() & "/") + pr.GetMonth(dt).ToString() & "/") + pr.GetDayOfMonth(dt).ToString()
موفق باشید.